Did you "Format Data"? You should try to install the ROM version where you created your backup and boot to system at least once. Then try to restore your backup in TWRP.
I tried to restore a backup of the rom and twrp I used to make the backup. There shouldn't probably be such an issue. And no, didn't format data, that's not how I restore my backups (otherwise each time I'd ~have to move ~220gb of data from my pc to phone....).
Almost the same thing was happeneing the previous time I tried to restore a backuo eith this twrp, but had formated the data partion eithout being able to restore it, leaving my phone factroy reset...
EDIT:Gonna try something weird: boot into the twrp with fastboot insteadof using the menu (the same twrp is flashed) (Edit:didnt work..)
EDIT2:Ah you meant to flash the rom again, even if its the same? OK, trying it. Edit: Didnt work too... That new twrp has caused me ~more problems than the previous one did in ~3months... I might just flash the 1206
EDIT3:I just reflashed the new rom and setted up magisk and LP again. At least they seem to work. I'll probably just continue with the power hungry gallery app till the next version...