Database Develop

[How-To] Upgrade/Downgrade any MATCHING ROMS without losing /Data

Hello
My name is Alvin and I really want to help the people who are new to Android hacking/rooting/flashing/roming<made that up . This post may not be interesting or super helpful, but I want to help people with a question that's not usually mentioned.
Upgrading/Downgrading, that's the Technology world right now. It's important people know how to keep up by upgrading without having to lose all their data.
Upgrading/Downgrading Difficulty Level: 2
(Scale of 1, being Beginners, to 10, being a developer)
To upgrade a ROM without losing data, you must me under these certain circumstances,
The ROMS match. THAT'S IT. Well what do I mean by "Rom Matches"???
The /data has to be compatible with the newer ROM.
The ROMs that are not compatible with the same data.
NC Stock to any other ROMS
THE DATA MUST BE WIPED BOTH GOING FROM STOCK AND GOING BACK TO STOCK. THE DATA IS NOT COMPATIBLE.
The ROMs that ARE Compatible:
CM7<>CM7
CM7<>CM9
CM7<>CM10
Custom ROMs<> Any CM ROM.
Note: Downgrading the Android OS and keeping Data is fine, but some items may be broken or incompatible after being modified in a newer Android Version.
NOW you read all the circumstances and determined that your Nook Color is OK to upgrade+keeping /data partition, here are instructions if you don't already know them.
Open any type of Recovery. CWM or TWRP. SD or Emmc.
Go to Mounts and Storage at the bottom
Carefully select Format /system
Next, select format /cache
Now, we are leaving the /data alone.
Click Back or use the power button to do so.
Click Install Zip from SDCARD.
Find your .zip file that you want to flash to upgrade/downgrade your Nook.
When finished, you may apply GApps which is optional. GApps was formatted with /system. If you need to find gapps, go to: goo.im
Reboot and the New ROM should look like it was used before by you.
Note: The location of these instructions are based on C.W.M. All instructions are same on other recoveries.
If this post helped you, I would appreciate a thanks because it would make my day.
If this post provides any false information, typos or errors, please tell me so because this is a great learning experience for me.
If there are any questions, I will answer them withing 48 hours. Valid till 11/4/12. After that I'll check periodically.
P.S I love smiley faces.
Sources: Picture from neown.com

Hey -- I'm just about to try these steps. It seems really self-explanatory to me, I'm more than a beginner but not quite at developer. I'd say I'm like a 6 or 7 in your list.
However, the one thing I haven't tried yet is upgrading to a newer ROM. I flashed Nameless v2.0.2 for the HTC Desire C and now they're at version 5. I just did a FULL backup using CWM Touch for the Desire, and I'm about to do what you suggest. I have a custom lockring, battery icon and boot animation, I guess I'll just have to push those three things back on afterward? I think everything will go smoothly, I even have a separate SD card to flash from ^^
Anyway, I guess that's not really a question... I just want to make sure these steps apply to any ROM... but logically it seems like it would.
-AC

Hey, if i downgrade my rom (Android N) with only remove the system, and install the lower rom (Android M) is it will delete the installed application and the data too?

Full image backup without unlocking bootloader?

Hi,
Pls pardon my noob questions...
I just gotten my 3T about a week now and after spending over 3 days setting up everything from scratch (eg installing numerous apps and configuring them one by one, setup emails, sms, contacts, icons packs, settings, etc) and finally gotten the phone to a state where I am very satisfied, a question dawn on me - How can I do a full image backup so that if anything happens, I can do a full image recovery and get back the "perfect" state?
After doing so much reading, it seemed the full image backup is called a "nandroid" backup and I need to first unlock the bootloader and flash TWRP in-order to perform this backup. But my predicament is, if I proceed to unlock bootloader, then all my configurations, setups and data will be wiped. So it became a chicken and egg scenario.
And the 2nd problem is that, worst comes to worst I decide to bite the bullet and proceed with unlocking and flashing TWRP, when booting into TWRP can I select "read only" and not agree with modified system since I have no intention to root. Will this cause boot loop problem if it is "read only"?
Can "read only" state in TWRP allows me to perform nandroid backup and restoration later on?
May I skip the next step of flashing anti dm verity file / root? I don't really want to go root since I am very happy with stock OOS at the moment.
So the big question is, is there anyway out there in the universe where I can do as close as possible to a nandroid backup without going bootloader unlocking route as that is not an option for me as I can't afford to have all the data, settings and configurations wiped. I heard about Helium app which can backup app data but that's about it. Everything else has to be setup from scratch.

Zegnalabel said:
Hi,
Pls pardon my noob questions...
I just gotten my 3T about a week now and after spending over 3 days setting up everything from scratch (eg installing numerous apps and configuring them one by one, setup emails, sms, contacts, icons packs, settings, etc) and finally gotten the phone to a state where I am very satisfied, a question dawn on me - How can I do a full image backup so that if anything happens, I can do a full image recovery and get back the "perfect" state?
After doing so much reading, it seemed the full image backup is called a "nandroid" backup and I need to first unlock the bootloader and flash TWRP in-order to perform this backup. But my predicament is, if I proceed to unlock bootloader, then all my configurations, setups and data will be wiped. So it became a chicken and egg scenario.
Click to expand...
Click to collapse
Yes, a Nandroid backup is what you want, and yes, you need an unlocked bootloader for that, and yes, you need to wipe your data to do that. That's why it's highly recommended that unlocking your bootloader is the first thing you do as soon as you get your phone (though that's obviously too late for you). To help ease the pain, you can do an adb backup as described at http://forum.xda-developers.com/showthread.php?t=1678239. This will preserve most but not all of your stuff, and doesn't need an unlocked bootloader. Once you do that, you can unlock the bootloader, restore the adb backup, then take a nandroid backup.
Zegnalabel said:
And the 2nd problem is that, worst comes to worst I decide to bite the bullet and proceed with unlocking and flashing TWRP, when booting into TWRP can I select "read only" and not agree with modified system since I have no intention to root. Will this cause boot loop problem if it is "read only"?
Can "read only" state in TWRP allows me to perform nandroid backup and restoration later on?
May I skip the next step of flashing anti dm verity file / root? I don't really want to go root since I am very happy with stock OOS at the moment.
So the big question is, is there anyway out there in the universe where I can do as close as possible to a nandroid backup without going bootloader unlocking route as that is not an option for me as I can't afford to have all the data, settings and configurations wiped. I heard about Helium app which can backup app data but that's about it. Everything else has to be setup from scratch.
Click to expand...
Click to collapse
Yes, you should mount /system read-only. You don't need to root or disable dm-verity as long as you do that. (By the way, Helium is pretty much just a nice wrapper around adb backup.)

josephcsible said:
Yes, a Nandroid backup is what you want, and yes, you need an unlocked bootloader for that, and yes, you need to wipe your data to do that. That's why it's highly recommended that unlocking your bootloader is the first thing you do as soon as you get your phone (though that's obviously too late for you). To help ease the pain, you can do an adb backup as described at http://forum.xda-developers.com/showthread.php?t=1678239. This will preserve most but not all of your stuff, and doesn't need an unlocked bootloader. Once you do that, you can unlock the bootloader, restore the adb backup, then take a nandroid backup.
Click to expand...
Click to collapse
Many thanks Joseph for your advice! I really appreciate it! You're totally right, I'll do an adb backup followed by bootloader unlocking and TWRP installation. :good:
Yes, you should mount /system read-only. You don't need to root or disable dm-verity as long as you do that. (By the way, Helium is pretty much just a nice wrapper around adb backup.)
Click to expand...
Click to collapse
May I further check with you what are the limitation bring about when choosing "read only" when first enter TWRP? As in won't be able to flash ROM, flash supersu, etc thereafter?
Once again, thanks for your help, Joseph!

Zegnalabel said:
May I further check with you what are the limitation bring about when choosing "read only" when first enter TWRP? As in won't be able to flash ROM, flash supersu, etc thereafter?
Click to expand...
Click to collapse
All it means is that you won't be able to modify /system with file manager or the shell. Flashable zips almost all contain code that remounts /system read-write (as the TWRP screen warns you about). Also, you can always change your mind and make it read-write later (though the reverse is not true; once you mount it read-write, putting it back to read-only doesn't fix anything unless you reflash the ROM).

Many thanks Joseph for your sound advice.
After taking some time to read through all the links and sub-links getting to know the varied means of backups available, I have decided that my backup strategy will be as follows since non of the methods offer comprehensive backup and a mixed of the lots will be required to get as fool-proof as possible, before embarking on a data wiping journey with bootloader unlocking.
(i) I first perform a backup using google native backup and restore function under setting no matter how limited it is, to be use as a safety net.
(ii) Next, adb backup. The limitation with adb backup is that since Android 6.0, it obeys AndroidManifest.xml and will not backup data of those apps which has android:allowBackup set to false. The challenge is, I will be held in the dark which app falls into this category when performing adb backup and won't know until after I had done the actual restoration. Its like a blackbox you won't know what you gonna face until the aftermath had hit. Therefore to get around this, I'll be using Helium app (a wrapper around adb backup) instead of the actual adb backup since both methods refer to AndroidManifest.xml when deciding which app data it can or cannot backup. And Helium shows exactly which app it can backup vs that which it can't. Good info there for a start.
After installing Helium and activating it via PC client, I found out it does backup:
A) SMS and call logs
B) User dictionary
C) Accounts
D) Bunch of apps and their data
List of apps and data it can't backup:
1) Contacts
2) browser bookmarks
3) Calender
4) System settings
5) APNs
6) Homescreen shortcuts
7) Widgets
8) Alarms
9) Photos
10) Music
11) Videos
12) MMS
13) Google AUTHENTICATOR!!! - I have over 15 profiles that I'll have to re-setup one by one... what a nightmare.
14) Line
15) Whatsapp
16) wechat
17) Signal
18) Nova launcher - luckily its setting can be exported and backup via the app's functionality.
19) QQMusic - all my thousands of songs! - even if I back this up manually using ES explorer the app's internal linkage between playlist to songs will be broken. Will have to re-download all the songs to repair linkage and this means wasting another month of subscription fees for songs re-download. This is one of the most problematic app but it has DTS plagin which makes your music sound fantastic even with cheap earpiece, so I am putting up with it.
20) Skype - not much chat in there so that's fine to start over.
(iii) After backing up the limited stuff using Helium, I shall proceed to use another app to backup (1) to (12). And that app will be "MyBackup" (https://play.google.com/store/apps/details?id=com.rerware.android.MyBackup&hl=en). The app developer confirmed in its app's features that (1) to (12) are supported. Note "MyBackup" does not backup any app data at all when device is not rooted therefore step one using Helium is still necessary.
(iv) Next, to circumvent the limitation with failure to backup app & data for (13) to (20), my initial thought were to patch each app's manifest using this method (https://forum.xda-developers.com/an...g/guide-how-to-enable-adb-backup-app-t3495117). But then, as I studied further, I realized another chicken and egg scenario. That is, the decompiling, editing, recompiling and signing of the patched apk would need to take place first before using the app and not after. So in another word this method with each newly patched app will not seemlessly replace the existing app but rather the existing app will first have to be uninstall before the patched app can be installed, and that very act would mean losing existing data altogether.
To install on android the patched apk, you must first uninstall your previous version, and this is because the key used to sign the apk is different. If you try to install one app itself with a different signing key, you will get this error: [INSTALL_FAILED_ALREADY_EXISTS] [Unquote]
Given this ****ty situation, I guess I am still hesitant and not ready to move forward with bootloader unlocking. Sigh...
Click to expand...
Click to collapse

Desperatly need to get data out of Huawei P10 VTR-29 (Possible soft-brick)

Hi!
!! This is quite serious! I need to get my data (pictures, videos) out of my phone, which is possibly soft-bricked.
I did the following in hope of more usage opportunities with my new phone:
[Unlocked bootloader + Rooted it]
1. installed TWRP following this guide https://forum.xda-developers.com/p10/development/testers-twrp-t3585256;
2. rooted following this guide https://forum.xda-developers.com/p10/help/root-huawei-p10-p10-t3589946;
3. installed few apps like greenify, wi-fi hacking apps etc, and everything was good.
BUT then 1 app (don't remember which) requested that it needs SuperSU and not the one root permission app that I had. So it asked whether I want to install it. I thought - yes, why not. Then it said that before it can install SuperSU it needs to uninstall previous permission app - I clicked OK. Then it kind of started, but then failed the installation. Ok, I kind of closed it and there were no problems. But after next restart of the phone it was stuck on boot process..
I dont really care about the phone, but data on it is so important. I tried sme fast hend methrods to boot it, like wiping catch, dalvik catch, but it did not work out.
Next I looked for possobilities to rescue data, but I didn't succeed.
Easiest mentioned option - to enter twrp and connect via usb seemed promising, BUT data are shown encrypted.
Please see the picture - I tried to be as precise as I could, so that you can understand the situation.
! I can beckup all data to micro sd card, but would it decrypt after new install of stock rom (e.g. from eRecovery that Huawei provides) and allow access or not?
Please help me. I am willing to have 1-on-1 skype chat and give some donations for this as it is so important.
To mention: Rescue apps like EaseUS seems to be useless, because they state to recover data from bricked device, but then after installing soft it askes to allow usb-debbuging, but c'mon, it's not booting up.. .
So,
1. Is there a chance to recover data?
2. Is it a good sign that 16GB of data are showing even if files are shown encrypted?
3. data are also showing on pc, when connected on twrp, but also encrypted.
Any help will be appreciated!

Additionally quite important question: at this state (possible soft brick + encrypted files), is there a chance that if I make a backup to MicroSd card of all the data and then take it our to reinstall rooted stock version of my android that later puting backup in will show my files that were backuped? Could ir be so that phone luckiliy decrypt them itself because it is the same phone? Hope this is clear what I mean.

OK, hopefully all is not lost.
First things first, be REALLY careful. If you start applying factory images, wiping things and generally messing about, if you don't know what you're doing you're putting your data in a lot of danger - Huawei devices do things in weird ways, so be super sure you know the consequences of what you're doing.
Now that's out of the way... it sounds like you haven't done anything to wipe the data. Also, you've already previously unlocked the bootloader which should put you in a good situation. You need to discount TWRP as a potential solution - there is no working decryption for TWRP yet on the Kirin 960 devices and from conversations I've had, it doesn't sound like that is imminent.
What it sounds like has happened is that messing about with root has messed up something on your system partition. Which should be fixable!
As a first step, this is what I'd do.
- Check which version your phone is on if you don't know already (you should be able to find this in ' /version/special_cust/VTR-L09/hw/eu/prop/local.prop')
- Find a full dload zip for the appropriate version (use FirmwareFinder if needed)
- Download the zip an extract the dload app
- Use splitupdate to split the images out of the dload
- Boot the device to bootloader ('adb reboot bootloader' or power on with cable connected and volume down pressed) then do 'fastboot flash system SYSTEM.img'
- Flash BOOT.img too
- Try booting
Hopefully this will fix it, but at the very least it'll get your system partition back to a stock state.
Let me know how it goes. Good luck!
P

[RECOVERY][TREBLE] TWRP 3.2.3-0L v1.3 Labs Mod for the ZTE Axon 7

- T W R P 3.2.3-0L [Labs Mod] -
The Swiss Army Knife TWRP Mod for the Axon 7​
INTRODUCTION
This was a long term project that I have been using for a long time. I created some scripts to make it easier and faster to flash new roms and quickly restore the daily driver configuration after a testing session. For easier access I modified the TWRP interface to add direct access to the scripts. They had many problems but they were good to me since I created them and I knew how to used them well, but they were not ready for other users.
But the time has come and I have cleaned up most of the annoyances in the tools and in the UI. I have named it "Labs Mod" since it allows me to have my flashing lab on the go, making it extremely easy to switch to different configurations, or recover the daily driver configuration in a few minutes. I believe it is free of major bugs and now I can concentrate on adding new scripts, and more options to the current scripts.
FEATURES
On top of the latest improvements introduced in the official TWRP 3.2.3-0, this mod offers the following added features:
Full vendor partition support (mount, format, wipe, partition image flash, TWRP backup and restore).
Integrated Bootstack backup and restore.
Modem firmware image flash
Reboot to EDL
Button to enable device mapper verity (DM-Verity) enforcing
Button to disable the eMMC write protection (disemmcwp)
Backup/Restore internal storage to the TWRP Backup folder in the external SD. Ensure you have enough free space, free space check is not yet implemented.
EDL backup zip creation. Dual zip use since the resulting zip can be installed using TWRP from the phone or using MiFlash from the computer. It offers the following package creation options:
OS: Operating system (boot, vendor and system).
GPT: Partition table only.
CONFIG: Device config data (IMEI, SN, MAC, etc).
BOOTSTACK: Boot firmware without modem.
MINIMAL: Includes GPT+bootstack+modem+recovery.
EMERGENCY: Minimal + device config.
FULL: Minimal + OS.
FACTORY: Includes Full + config.​
Integrated Treble PARTY tool for creating and removing the vendor partition. Vendor partition is required for Treble ROMs. Removal is required for flashing old non-treble roms.
Lockscreen security removal. Removes password, pattern, fingerprint, etc... (in case you forget your password or the security descriptor gets corrupted).
Google account binding removal (in case you want to wipe from within recovery and test with different google accounts).
Bootloader unlock message removal.
New! Expand OS partitions (Vendor and System) to fit the whole partition. Useful for expanding the GSI filesystem for having space for adding GApps or moving apps to system.
New! Deep Wipe function performs a low level wipe of the partition data, erasing the remaining the portions of the eMMC that stored the partition information.
REQUIREMENTS
You need an unlocked Axon 7
INSTALLATION
WARNING, THIS SOFTWARE COULD WIPE ALL THE DATA IN YOUR DEVICE, INCLUDING THE INTERNAL STORAGE.
IT REQUIRES TWRP CUSTOM RECOVERY IN AN UNLOCKED DEVICE, OTHERWISE YOUR DEVICE COULD BE BRICKED.
!!! Whatever you do, it is at your own risk !!!​
Follow these steps:
1. Download the TWRP Labs Mod image to your External SD card.
2. Boot to TWRP and select the Install option in the main manu.
3. Tap on the install image button and select your external SD. select the image file you downloaded, select the recovery partition and confirm.
4. Reboot to recovery again to ensure the changes are applied properly.
DOWNLOAD
TWRP_3.2.3-0L_v1.3-Axon7-Labs_Mod.img Flavor of the mod using the official TWRP 3.2.3-0 Kernel binary (Quick boot even when using F2FS, full ADB support, NO B12 Oreo encryption). Use this if you do not plan on using device encryption. Please note that you won't be able to use any tool of this version if your device is encrypted.
TWRP_3.2.3-0L_v1.3.B12-Axon7-Labs_Mod.img Device encryption enabled flavor of the Labs mod. It use the 3.2.1-8 TWRP Kernel binary (Long boot when using F2FS, NO ADB support, B12 Oreo encryption). Use this one if you use device encryption. Please note that this flavor doesn't support adb interface.
NOTES
1. I do not have the time and expertise to dig into kernel hack so this is why I do not provide a unified kernel with fast F2FS boot, ADB and B12 encryption. Probably people developing kernels could help on this issue. It would be nice having a kernel with proper F2FS boot support, B12 encryption and ADB interface. Until then, there is no other way than having 2 flavors depending on the features we require.
SOURCES
C'mon, all of them are scripts!!! the sources are at glance. Use them in your projects but don't forget to give credit to the source !!!
CREDITS
@NFound for the recovery kernel binary supporting Oreo B12 encryption.
@someone755 for the keycheck binary I use in my scripts.
@Chainfire for the TWRP install script hacks.

I hope you enjoy it as much as I did creating and learning throughout the enlightenment journey.

Nice.
Any info on the scripts that are included?

voetbalremco said:
Nice.
Any info on the scripts that are included?
Click to expand...
Click to collapse
Well, all of them are Bourne shell scripts. Some of them are stupidly simple such as those in the Reboot menu, and others in the Advanced > Oki Labs menu are very elaborated, specially:
- PARTY tool: for creating and removing the vendor partition. I released it a few days ago as a separated tool that could well work in other devices.
- EDL backup: for creating EDL flashable backups of a configuration. This tool will probably require a full thread due to the concepts involved. The big feature is that the generated zip can be also flashed using any TWRP.
- Internal Storage Backup/Restore: TWRP doesn't offer a straightforward solution for backing up the internal storage, since it is excluded from the data backup, now it is possible to create a backup and restore the contents of the internal SD in case you want to mess up with the userdata partition. Now this script creates a set of files under the TWRP/backup folder. I am planning to add the possibility of having different backup folders, the same way the GUI treats the data partition.

That is looking very sweet!!!
I'm excited, nice work man!

This is just fantastic!

Well, the non b12 version can't decrypt my device, running los 15.1
also, the lab options did nothing, and when I pressed on PARTY the recovery froze on me.
Hmm.

nfsmw_gr said:
Well, the non b12 version can't decrypt my device, running los 15.1
also, the lab options did nothing, and when I pressed on PARTY the recovery froze on me.
Hmm.
Click to expand...
Click to collapse
Well, that's why in the OP I provide 2 flavors of the mod. If you require decrypt then you have to use the B12. PARTY will not work either if your device is encrypted and you are using the 3.2.3-0L. In your case, using device encryption, you have to use the 3.2.3-0L(B12). You will have all the functions except for ADB. PARTY will work fine too.

Oki said:
Well, that's why in the OP I provide 2 flavors of the mod. If you require decrypt then you have to use the B12. PARTY will not work either if your device is encrypted and you are using the 3.2.3-0L. In your case, using device encryption, you have to use the 3.2.3-0L(B12). You will have all the functions except for ADB. PARTY will work fine too.
Click to expand...
Click to collapse
Got it.
I thought the B12 version was for stock-based ROMs.
Okay I'll flash the other one once I get home, thanks.

nfsmw_gr said:
Got it.
I thought the B12 version was for stock-based ROMs.
Okay I'll flash the other one once I get home, thanks.
Click to expand...
Click to collapse
I'll clarify it a bit more to avoid any misunderstanding. Sorry about that.

Oki said:
I'll clarify it a bit more to avoid any misunderstanding. Sorry about that.
Click to expand...
Click to collapse
Thnx for this tool ! I'll test that this weekend.
It would be great if you'd make a small guide on this with a couple of situations / a possible indepth review with screens / what's possible and what's definitely not possible with this twrp tool.
Anyway seems very promising :good:

Sheesh...i have no external sd card

I have garde flashed your TWRP_3.2.3-0L (B12) -Axon7-Labs_Mod.img but this version says when starting in twrp that my password is wrong. the version 3.2.1.8 of nfound unlocks my password quite normal

Excellent Job! I can't wait to get back my Axon 7 from RMA Services. I'm just going to need sometime to get this running coming from stock MIflavor.

Found bug. Installed the ADB version (thanks Cthulu!), wanted to check the functionality.
Went into the Storage Backup and my phone froze. Rebooting from ADB worked.
EDIT: tried to reproduce the issue - same thing happened 2nd time.
EDIT2: It freezes at any option in Oki Labs

docentore said:
Found bug. Installed the ADB version (thanks Cthulu!), wanted to check the functionality.
Went into the Storage Backup and my phone froze. Rebooting from ADB worked.
EDIT: tried to reproduce the issue - same thing happened 2nd time.
EDIT2: It freezes at any option in Oki Labs
Click to expand...
Click to collapse
I can't duplicate the issue. Are you sure you downloaded it properly? Do you have an SD card? The backup requires an SD card with enough space. Checking for free space is in the todo list for this weekend.

raystef66 said:
Thnx for this tool ! I'll test that this weekend.
Anyway seems very promising :good:
Click to expand...
Click to collapse
Not good enough!

It is downloaded properly. SD card has more than 100gb free space.
As mentioned in edit it is any option that I used in Oki Labs menu that froze my phone

docentore said:
It is downloaded properly. SD card has more than 100gb free space.
As mentioned in edit it is any option that I used in Oki Labs menu that froze my phone
Click to expand...
Click to collapse
What option are you testing? the Storage Backup? What format are you using in your SDCard? Does it happen at the beginning or after a while? Is there any file under TWRP/BACKUPS/STORAGE in your Micro SD after the failure?

@Oki this is amazing. Thank you.
Is it possible to use the recently released kernel sources from los15 to solve the issue of needing two revisions?

ROG 2 phone soft bricked

Hello,
today I did have a strange experience with my ROG 2 and my best guess is that there is some UFS problem, but a second opinion or ideas are welcome.
During a bike ride when I was wifi scanning (apps: "Tower collector", "Radio Beacon"), navigating and listening to an audio book, the phone just went dark. I thought from previous experience on a Note 3 that it might have overheated. Pretty much stress proofed from the previous phone.
Yes - it was warm in its bike pocket but really not overly hot.
The phone is an ebay buy 2 months old and has been ever since with omnirom, stable so far. I only noticed that the RGB LED here has no blue light, but I plainly did not care.
I tried to boot it after some 10 minutes again and the phone would not go past its omnirom boot screen until it reboots after some time, boot loops.
30 Minutes later at home I wondered then what is going on, and I copied off the TWRP backup from the phone I took two days ago, just in case.
I then tried to restore the same backup, but the phone switched off during restore after ~30%. This was reproducible, so I thought this may be something with the backup, maybe I cannot restore a partition. When I restore I had all partitions marked and I tested them one by one. The restore of single partitions worked, one by one, except vendor as it was marked read only and data as it failed unpacking (my recent backup then is dead?).
I then tried formatting the partitions, so "data", originally f2fs. I lack experience with journal recovery on f2fs so went to ext4. System was ext4 and was just wiped. I lost of course other data on the internal storage so tried to restore again with my copied backup. It restores, but it cannot boot and just bootloops. I now formatted all partitions, including vendor.
Finally, I tried downloading omnirom again and installed it. It won't boot, it doesn't even get to the boot animation, but just boot loops.
I reformatted data back to f2fs. But no change here.
Trying more: lineageos won't flash for unknown reasons, it immediately dies as "Error installing zip file". Checksum of the downloaded zip is correct.
I downloaded a stock rom and installed it. This is now the best result so far - It does want to boot.
Here I get a boot animation and this incredibly lame "tching" sound (it is a phone, not a sword...). But it also stops there and never continues. Yes, first boot takes longer, but not 10 minutes.
Any ideas what else to try with this phone?
So far, I can boot twrp via sideload and interact with it fine. But that will be it; ran out of ideas.
Happy for suggestions.
Gaya

Use raw firmware to restore everything.
Install latest firmware zip on both slots.
After installing custom roms go to wipe -> format data by typing yes. Otherwise rom wont boot

thanks for getting back, If by raw firmware you meant the ASUS stock, I did. Not sure why data wipe after installation or double install to a/b partition would make a difference, but in the end I am new to this a/b concept, looks though like standard dual boot to me. Tried it, but no difference.
- installed asus firmware to inactive B
- switched to B partition
- installed asus firmware to inactive A
- wiped data
- started, so far same behaviour after 15 minutes of waiting (boot animation with sound, then it repeats boot animation until ...).

There are Two kind of rom raw firmware (used to restore bricked device) and recovery rom (zip file we use for update)
Raw firmware will flash ROM to both the slots, while recovery rom only flash to one slot. So you need to Only select reboot to recovery after flashing ROM to switch to the updated slot.
No, stock rom is not exactly raw firmware. RAW firmware uses EDL mode (in bootloader) to flash the stock rom. Download A10 raw from here version .90.
when extracting it you will see some files.
Steps To flash Raw:
* enable usb debugging in phone.
*connect the phone via side port to pc
open command prompt and run this command
adb devices
adb reboot bootloader
Now go to the folder where you extracted the raw firmware & run "flashall_AFT.cmd" as admin
wait [there will be no output]. After 15 -20 mins your device should boot. If you have any old version stock rom data the phone will carry the data to new version. If you have any custom rom/ updated version of stock rom data, it will ask to factory reset, so do that.
wiping is not exactly formatting so do it the right way
Why format: the one where you format by typing "yes" .If you switch between Roms ( stock to custom or vice versa) and go back to older versions (v .100 to .60) the old/previous rom data cant be used with new one so you must format data.
when formatting is not necessary : If you want to upgrade both stock images (version .90 to .100) & custom rom (v 1 to 1.2) i.e., flashing stock rom and then custom rom over it, you dont need to format data because you can reuse the data from custom rom to updated custom rom.
A/B device use two partition instead of one. so the upgrade can happen in the background. On restart you will switched to updated slot. So room for error is less.

The wiping here should be the same as formatting, as it is running the mke2fs (as per TWRP settings). But raw rom I do not have (I believe).
The link you have there seems broken, could you repost it again?
I did download the stock ROM earlier from ASUS directly, to not violate policies, HTTP links etc, here is only the path on asus . com
pub/ASUS/ZenFone/ZS660KL/UL-ASUS_I001_1-ASUS-17.0240.2103.75-1.1.229-user.zip
That is the one I installed via recovery. Am not sure what is in your mentioned flashall_AFT.cmd though, but suspect some adb sideload at least.

I eventually succeeded, but of course would liek to know
1) why
2) what happened?
I did follow a video about flashing the stock rom, basically as you explained (factory reset and data wipe), twice to a and b partition. That made the device bootable. Why is this needed?
I tested wiping system again (I am used to doing clean flashes) and installed omnirom again, and it failed booting.
I installed again the a/b with stocks, factory reset and data wipe and installed omnirom as dirty flash. All is well.
Now I was able to restore my backup finally without the device switching off and it did not complain about the data backup. So finally I am with my phone again rom and copy data to my fresh partition.
as to 1) why?
I understand a/b partition as sort of windows/linux dual boot with a more separate bootloader maybe. So I do not see the point in flashing the stock rom twice or in rendering the device unbootable when wiping system.
and as 2) what happened.
I may only guess: I did an omnirom upgrade 2 days earlier that worked fine and was the reason for my nandroid.
During my ride, the phone had some whateverissue and rebooted. I am unsure whether i tested booting but assume that after the upgrade it flashed to the other partition and it was not bootable. It does not make sense as this would make a/B partitions rather hard for custom rom makers, e.g. people complaining all the time.
Other guess: there was a file system issue with f2fs. Problem with data partition seems to cause bigger issues.
When I flash to ext4 after testing the bootable rom with a wiped data, it would not boot anymore. After factory reset again, it mke2fs the data partition again, back to f2fs and the device booted again happily.
Thanks for the help. Happy to know/learn more about this issue, as I would love to prevent or handle them quicker with more of I know what I'm doing.

Android Dual Partition (A/B) is made for seamless updates i.e, Dual system/vendor partition but uses same data partition. Lets say you are currently in slot A when you apply system update the slot B gets updated. As always rebooting the device switches to the B partition after update. & further update flashes the system to the A partition.
Basically there is no need to flash stock rom twice, unless you are coming from stock [one partition might be in higher firmware version than other] or there is new stock version with some minor/major upgrades to firmware files.
Our custom ROMs are not stand alone, Mostly it only replaces the system files and keep the vendor same as stock. (also this keeps the ROM update file size to be minimum)
you might even have different version of Android in A/B partition.
Here is a scenario on How A/B works:
Say you are currently using your device in B-slot and A9 so partition on slot-A will be A9 partition slot-B be A9. After that you are doing system update to A10 from System update (not via TWRP)
now you will have A10 on slot-A and A9 on slot-B.
then you want to go to custom rom, so you flashed say omni on A-slot and rebooted & it will surely work.
After that you are using inbuild system update from custom rom any applied it. now the system update will overwrite the A9's system files but (the device specifically needs A10s vendor to work properly). Now comes the fun part i.e., soft brick, boot looping, and corrupt images
That's why you have to flash latest stock to both A and B slots, and overwrite them all with system files from custom rom (also should be flashed once in slots A and B) to get neat experience from custom ROMs.
If you understand what was written above, then you will know the reason behind soft brick.
stock rom flashed only once (firmware image variation may affect stability)
custom rom only flashed in one slot (switching slot will boot loop device)
Not using Reboot to recovery to flash (you will be flashing to the same slot over and over & thus rebooting will boot loop)
Not formatting data ( Just Maybe, your custom ROM and stock uses different file system for data partition)
For Raw files search "ASUS rog 2 RAW firmware images" those files will be around 3 GB in size.