I already tried that method, but there were two major problems:When you create and restore a TWRP backup (as example because you tried out a custom ROM and saw that it's not good) you'll be greeted with: a) A "enter...forums.oneplus.com
1. I don't know how to get to TWRP without wiping the data on the phone (hardware buttons) or through 'adb reboot bootloader', which i cannot authorize, because on my backup I didn't have "transfer files" as the default usb protocol and without logging into the system I cannot authorize it.
2. When I was trying out different versions of Lineage to see if the problem persisted, when I was on 18.1 I tried to reboot to TWRP through adb, then wipe, flash Lineage, reboot into recovery when I was in TWRP, then restore the Data partition, reboot into recovery while in TWRP, and then reboot into recovery from TWRP again, to finally wipe the files mentioned in that guide and in this thread under /data/system, but I couldn't find any of those files. So I'm not sure if it is only a problem cause by the files being moved around in Android 11, or even from a previous version, or if the method of rebooting to recovery from TWRP itself wasn't enough to load the data.
But I didn't lose much, since I had multiple offsite backups for "important" things and so I went ahead and reapplied the settings and reinstalled previously used software yesterday evening. Still, if you have an answer for any of the aforementioned questions, I'd like to hear them. Thanks.