I'm doing this with very basic understanding of what I'm doing/being recommended to do. Is adb backup --twrp a command or twice different things as in 'adb backup' to computer and twrp is done on the phone?
That would be a command you have to run in a command line window on your computer. Again, after the --twrp parameter, you can pass the names of the partitions you want to have backed up, which would probably be data, system, recovery and boot.
First, of course, you have to
install adb, if you haven't already. But if that's too complicated, it might be easier to make a full backup in TWRP and then copy it over to your computer. adb backup --twrp basically saves a step and you don't have to have sufficient space on your phone for a full backup
My plan is to copy the important data like audio files and photos to my laptop, then use use migrate to make a copy plus twrp backup. I should be fine after that I think.
That's always a good idea, even though wiping data in TWRP should not touch your internal files.
I'm just hoping my root and magisk doesn't go when I reinstal OOS 9.0.6 as I want to try to edit my system to see if I can force vowife to work.
I don't know, I never used it. I'm happy with LineageOS. I guess you can re-flash Magisk trough twrp and then in your running system, you can re-install the MagiskManager apk. But I haven't tried it.