Database Develop

TWRP backup question: system vs system image

Thanks to everyone here up front for all the awesome help available here.
I just got my Nexus 6, and no issues unlocking bootloader, installing custom recovery (TWRP), getting root and flashing ROMs/zips (currently loving Pure Nexus with xposed).
My question is regarding backups. When you backup your current setup, most of the information I've found don't show the "System Image" partition under the "System" partition when you go to make a new backup. It's quite large, and I was wondering exactly what that is, and if you need to include that in your backup. Anyone know of a helpful link that explains the partitions?
Also, if you make a bunch of backups, and move them to your computer, does that make things harder if you want to restore from a backup? Can you restore from a backup on your computer just as easily as a backup on the phone's internal storage?
Thanks again
Edit (1/15/2016):
Thanks to RMarkwald and scryan for the quick responses and info. So it seems that the system image isn't going to be needed, and backing up System, Data, and Boot will be good enough for normal backup of the phone/rom before trying something that might break the current setup.

giantninja said:
Thanks to everyone here up front for all the awesome help available here.
I just got my Nexus 6, and no issues unlocking bootloader, installing custom recovery (TWRP), getting root and flashing ROMs/zips (currently loving Pure Nexus with xposed).
My question is regarding backups. When you backup your current setup, most of the information I've found don't show the "System Image" partition under the "System" partition when you go to make a new backup. It's quite large, and I was wondering exactly what that is, and if you need to include that in your backup. Anyone know of a helpful link that explains the partitions?
Also, if you make a bunch of backups, and move them to your computer, does that make things harder if you want to restore from a backup? Can you restore from a backup on your computer just as easily as a backup on the phone's internal storage?
Thanks again
Click to expand...
Click to collapse
According to TWRP in regards to System Image: The Team Win Recovery Project has released version 2.8.7.0 of its custom recovery, known simply as TWRP. This update brings a system read-only option that's intended to help you make a pure backup of your system image that you can later flash to receive over-the-air updates after having rooted or ROMed your device.
If you move backups to your computer, you'll either need to move them back to the internal storage of your phone or USB stick to use USB OTG to restore backups.

I already rooted my phone. Where can I get the pure system image now that I can later flash to receive over-the-air updates.

rocco24 said:
I already rooted my phone. Where can I get the pure system image now that I can later flash to receive over-the-air updates.
Click to expand...
Click to collapse
why would you want to unroot your phone, loose all your info, to flash a factory image, just to get an ota? why waste your time??? you can remain rooted, grab the system.img from a factory image, flash it with fastboot, not loose any info, then just reflash SuperSU and a kernel, and be updated. factory images are here https://developers.google.com/android/nexus/images?csw=1#yakju

simms22 said:
why would you want to unroot your phone, loose all your info, to flash a factory image, just to get an ota? why waste your time??? you can remain rooted, grab the system.img from a factory image, flash it with fastboot, not loose any info, then just reflash SuperSU and a kernel, and be updated. factory images are here https://developers.google.com/android/nexus/images?csw=1#yakju
Click to expand...
Click to collapse
Thanks for the explanation. I meant the system.img not the full factory image my bad.

rocco24 said:
Thanks for the explanation. I meant the system.img not the full factory image my bad.
Click to expand...
Click to collapse
the system.img is in the factory.img, just like the boot.img, cache.img, etc..

Nailed it thanks

RMarkwald said:
According to TWRP in regards to System Image: The Team Win Recovery Project has released version 2.8.7.0 of its custom recovery, known simply as TWRP. This update brings a system read-only option that's intended to help you make a pure backup of your system image that you can later flash to receive over-the-air updates after having rooted or ROMed your device.
If you move backups to your computer, you'll either need to move them back to the internal storage of your phone or USB stick to use USB OTG to restore backups.
Click to expand...
Click to collapse
Ok, cool... So, if I want to try another ROM out, when I backup my current setup (Pure Nexus with xposed and some themes etc...), should I just backup System, data and boot? or should I backup that System Image as well? or is that System Image the snapshot of the stock ROM that the phone came with?
Thanks again

giantninja said:
Ok, cool... So, if I want to try another ROM out, when I backup my current setup (Pure Nexus with xposed and some themes etc...), should I just backup System, data and boot? or should I backup that System Image as well? or is that System Image the snapshot of the stock ROM that the phone came with?
Thanks again
Click to expand...
Click to collapse
Don't need the system image.
IIRC the system image will give you and .img file of your backup, you could then fastboot that to restore system. (I think... never tested. I believe you can do install and switch from zip to img as well...)
But for just a standard backup with TWRP so you can restore later if you have any problems... Just do as you said with the normal System (os), data (apps & app data), boot (kernel)
Not really sure who is using the system image option, or why...

scryan said:
Don't need the system image.
IIRC the system image will give you and .img file of your backup, you could then fastboot that to restore system. (I think... never tested. I believe you can do install and switch from zip to img as well...)
But for just a standard backup with TWRP so you can restore later if you have any problems... Just do as you said with the normal System (os), data (apps & app data), boot (kernel)
Not really sure who is using the system image option, or why...
Click to expand...
Click to collapse
Awesome. That's what I was thinking, but I've been wrong before, so it never hurts to verify.
Thanks!

Opps wrong thread... Lol

Do any of you know how to reduce the size of or remove the System Image partition on the phone? It's taking up over 4gb on my phone and preventing me from restoring my data partition since it's running out of space during the restore.

cstokes86 said:
Do any of you know how to reduce the size of or remove the System Image partition on the phone? It's taking up over 4gb on my phone and preventing me from restoring my data partition since it's running out of space during the restore.
Click to expand...
Click to collapse
I delete any foreign keyboards I don't need to reduce the system partition size. Delete /system/app/(GoogleHindiIME, GoogleJapaneseIME, GooglePinyinIME, KoreanIME). You can either mount system in TWRP and delete, or delete them with a root explorer if you're rooted.

JimSmith94 said:
I delete any foreign keyboards I don't need to reduce the system partition size. Delete /system/app/(GoogleHindiIME, GoogleJapaneseIME, GooglePinyinIME, KoreanIME). You can either mount system in TWRP and delete, or delete them with a root explorer if you're rooted.
Click to expand...
Click to collapse
Thanks, Jim. I can wipe my main system partition to free up some space and then restore it later so I don't need to worry about tediously going through and removing unnecessary files. My issue is the "System Image" partition which is actually just over 3GB on my phone. I cannot seem to locate this partition and clear it out so I'm kinda stuck until I can figure out how to reduce the size of this partition ie clear out files from the partition either manually or entirely.

I'm in npd90g preview flashed via twrp.if I want official ota
Just flash system image of mm latest and this downgrade doesn't brick my phone ? Can I get ota? And what other should I flash with system image ? Boot ,data and recovery also ?

I dont no much english like othetr peopel
Promblem is i root my honor5x then device get so heat up . After that i deciede to reset it factory setting i have done it but now my device is stuk in twrp loop its not going back normal condition like factory setting plz help me ........ plz

@Shakil jamali: Wrong forum. Go to Honor 5X forum and ask again.

cstokes86 said:
Thanks, Jim. I can wipe my main system partition to free up some space and then restore it later so I don't need to worry about tediously going through and removing unnecessary files. My issue is the "System Image" partition which is actually just over 3GB on my phone. I cannot seem to locate this partition and clear it out so I'm kinda stuck until I can figure out how to reduce the size of this partition ie clear out files from the partition either manually or entirely.
Click to expand...
Click to collapse
Good question. Is this system image actually a partition? Or something TWRP does combining the system image part with a few others into one file? If it is a partition would it be possible to delete it and resize system partition to make use of the extra space? I'm on a nextbit robin stock 7.1.1. Sys image shows as 3,072mb.

For some reason, i cant backup my device through twrp because of error 255. I tried unticking system, then ticked system image and somehow the backup worked. My question is, is it ok to backup with the system image instead of system? What happens when i restore? TIA

soyti2x said:
For some reason, i cant backup my device through twrp because of error 255. I tried unticking system, then ticked system image and somehow the backup worked. My question is, is it ok to backup with the system image instead of system? What happens when i restore? TIA
Click to expand...
Click to collapse
First, for your 255 error, look at this post. Get rid of the corrupted file and a normal nandroid will work.
To answer your main question, you can use the system.img as a backup. It is intended for people who want an complete, untouched system backup to restore prior to attempting a OTA update.
An alternative approach to backup/restore that works very well in N6, is Chainfire's FlashFire.

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

Galaxy S8 boot loop after trying to install an older version of Magisk

First, I should point out that I'm just a user, not a developer or hacker. I'm posting this because I don't know where else to ask for help.
This will most likely look like the post of an idiot. But, oh, well, I did manage to mess up my phone, which means I am an idiot. So here it goes: I had 16.0 installed and I tried to install 14.0 from TWRP recovery mode. Basically, Magisk hide wasn't working very well so I wanted to see if it worked with an older version. Now my phone is stuck in a boot loop. It just shows "Samsung Galaxy S8 powered by Android" then restarts. I can boot into TWRP and connect the phone to the PC to access the storage this way, but I can't boot into the OS. Is there any way I can fix this, preferably without losing my data?
I tried flashing the official uninstaller, but I get the message "Update process ended with ERROR: 1"
Here's what the log says about the uninstaller:
Mounting /system, /vendor
-Device platform: arm64
cp: can't stat '/dev/tmp/install/arm64/.': No such file or directory
! Cannot find /data/adb/magisk
Updater process ended with ERROR: 1
I:Install took 1 second(s).
Error installing zip file '/sdcard/Download/Magisk-uninstaller-20180429.zip'
Updating partition details...
I: Data backup size is 32943MB, free: 2620MB.
I:Unable to mount '/usb-otg'
I:Actual block device: '', current file system: 'vfat'
...done
I:Set page: 'flash_done'
I: operation_end - status=1
I looked at the contents of the zip on my computer, and it doesn't have an arm64 folder. So the uninstaller doesn't work on arm64 phones?
Update: I managed to uninstall Magisk using a compatible uninstaller, but the phone still doesn't boot into the OS.
Update 2: if I have to flash the stock ROM, I'm planning to do the next thing: back up my data partition to an external hard drive with TWRP. After I flash the ROM and wipe everything, I want to reinstall TWRP and restore that backup. Would this cause any issues?

Yes, there's an issue on 64-bit devices with the latest available uninstaller. Use the next to last, here: https://github.com/topjohnwu/Magisk/releases/download/v16.3/Magisk-uninstaller-20180328.zip

Thanks. I've just left home and I'll be away for two days. I didn't take the S8 with me, so I won't be able to try any more fixes until Sunday. But I'll check then and update my post if there are any more issues.

Didgeridoohan said:
Yes, there's an issue on 64-bit devices with the latest available uninstaller. Use the next to last, here:
Click to expand...
Click to collapse
I managed to uninstall Magisk with that zip, but the phone still doesn't boot into Android.

vladone97 said:
I managed to uninstall Magisk with that zip, but the phone still doesn't boot into Android.
Click to expand...
Click to collapse
In that case, restoring the stock boot image manually might work. If not, a complete restoration of your device's stock setup might be necessary.
Your device's forum is likely the best place to get further help.

Didgeridoohan said:
In that case, restoring the stock boot image manually might work. If not, a complete restoration of your device's stock setup might be necessary.
Your device's forum is likely the best place to get further help.
Click to expand...
Click to collapse
I tried flashing the stock boot image and it still doesn't work. Stock restoration it is then.

Didgeridoohan said:
In that case, restoring the stock boot image manually might work. If not, a complete restoration of your device's stock setup might be necessary.
Your device's forum is likely the best place to get further help.
Click to expand...
Click to collapse
One more question, though: I backed up my data partition to an external hard drive with TWRP. After I flash the stock ROM and wipe my data, I want to reinstall TWRP and restore that backup. Would this work or would it cause problems?

vladone97 said:
One more question, though: I backed up my data partition to an external hard drive with TWRP. After I flash the stock ROM and wipe my data, I want to reinstall TWRP and restore that backup. Would this work or would it cause problems?
Click to expand...
Click to collapse
If you get your device up and running after the wipe and reinstall, you could always try restoring the backup. If it works, it works, and if it doesn't you can just wipe /data again.

Didgeridoohan said:
If you get your device up and running after the wipe and reinstall, you could always try restoring the backup. If it works, it works, and if it doesn't you can just wipe /data again.
Click to expand...
Click to collapse
Is there any other partition I should back up? That is, aside from the internal storage, which I've already taken care of.

vladone97 said:
Is there any other partition I should back up? That is, aside from the internal storage, which I've already taken care of.
Click to expand...
Click to collapse
Not if you're flashing back to stock anyways. Sounds like something is borked anyways so restoring anything might cause problems (including data). I would just start over. It's just data. Apps can be re installed. Contacts re sync.
I would start fresh, make sure it boots, make a full backup, then try restoring only data. Remember that /data may contain some of your old magisk stuff that may have added to the problem. So do that at your own risk. What data could be worth all that hassle?
Try to think of it like, if that phone got smashed, and you got a free replacement tomorrow. You'd survive right? Even without that data?
And definitely don't try to flash a magisk version that old over one that new one again.

vladone97 said:
Is there any other partition I should back up? That is, aside from the internal storage, which I've already taken care of.
Click to expand...
Click to collapse
Good advice by @madbat99.
Personally I only ever keep TWRP backups of the devices I test stuff on. But then I do a full backup of the device to have an easy way to get back to the setup I want.
On my everyday device I only keep a backup of the internal storage and messages (Signal). It's so easy to restore apps and other stuff anyway, so I don't really bother...

Didgeridoohan said:
Good advice by @madbat99.
Personally I only ever keep TWRP backups of the devices I test stuff on. But then I do a full backup of the device to have an easy way to get back to the setup I want.
On my everyday device I only keep a backup of the internal storage and messages (Signal). It's so easy to restore apps and other stuff anyway, so I don't really bother...
Click to expand...
Click to collapse
I did all that, but Magisk 19.1 still doesn't work. Some older versions work though. I tried Magisk 18.0, 18.0, 19.0 and 19.1. Only 18.0 and 18.1 worked. So I'm assuming there's a problem with the newer versions of Magisk?

With TWRP + Backups Working Now - Which partitions make sense to backup regularly?

Until now, no my rooted Samsung Note 3 I have automatic TWRP backups running every night. This just mirrors my paranoia that I will manage to screw up something and recovery via TWRP restore is often faster/easier/more complete than trying to do anything else. I do this using the OpenRecoveryScript and have always used this backup command:
backup DSBCR DailyBackup
Which gets data, system, boot, cache, and recovery. I plan to do the same now that I know to put the OpenRecoveryScript into /data/cache/recovery instead of /cache/recovery on my Note 3.
So my question here is what partitions make sense to backup on the V40? And by "sense" I mean something likely to change or get broken (by errant apps or, more likely, my own doing) AND having the ability to restore using TWRP restore from backup.
There are a ton of partitions on this device - most of which I know little/nothing about. I do know that the system and vendor partitions have duplicates and so those are not needed, I guess. And it seems that the OpenRecoveryScript backup command has no way to handle anything except the following anyway:
S: system,
D: data,
C: cache,
R: recovery,
B: boot,
A: and-sec,
E: sd-ext (I don't need the external SD)
So there would seem to be no way to get modem and all the others I don't know much about anyhow.
When I tried to use the same command as above, I ended up with only boot and data - which is a great start! I think I saw an error that system was not mounted so maybe that explains its absence - perhaps I need to mount it first in my script (which I never have had to do on my Note 3)? Even though my V40 is rooted with Magisk, I am making changes to system so I do want to back that up (so long as I can use it during a restore).
Does it make sense to try and backup recovery since things seem really different recovery-wise on this device? Same question for cache and boot?
Thanks for your tolerance of my newbie questions.

Well from empirical experience, it seems that there is no way to backup anything save boot and data. I was able to mount /system_root but that had no impact on backing up system. And I was unable to mount cache or recovery explicitly so those are out as well.
PS - for anyone using the old 123 special partition for backups, they are no longer supported. I have never used them but decided to try and see what happened - only messages that they are no longer supported.
Perhaps there is some other way to accomplish this? Suggestions welcome. Thanks
Thanks.

That I'm aware of recovery should backup as part of the boot partition....I could be wrong tho

Ainz_Ooal_Gown said:
That I'm aware of recovery should backup as part of the boot partition....I could be wrong tho
Click to expand...
Click to collapse
I guess that does make sense. Thanks. I am still trying to get my mind around the whole new situation (compared to my old Note 3).

Best way to restore all settings, apps, etc. when upgrading/changing ROMs?

I would like to keep everything else the same on my phone.
- I don't know if that means I'll have to backup/reinstall everything, if that happens automatically, or what.
- I have the following installed: TWRP 3.4.0.0, Titanium Backup Pro, Frija, Odin, ADB (?)
I currently have "ALEXNDR.N960FXXU6FTJ5" that I got here (based on Android 10)
I think it was from this thread: https://forum.xda-developers.com/t/...ase-v7-4-dex-gear-encryption-support.3847061/
If I want to follow those instructions, should I:
1) do a complete TWRP backup *first*?
2) follow the instructions to update the ROM
3) then restore from Titanium Backup?
As I understand it, the TWRP backup is *ONLY* if I want to restore the entire "disk image" and revert back to the ROM I have now, right?

You can use TWRP restore only if you mess something while flashing kernels, magisk modules, Xposed modules, etc .. it is also useful in your first OEM unlock to preserve vendor and ODM images so that you won't have to flash stock ROM again if something go wrong.
If you are asking about restoring apps, SMS and call logs, I highly recommend swift backup. Not for settings though. Personally, I stopped using titanium backup years ago since it is deprecated and last update was in 2019.