Running 10.8.0.4 I have the same problem.
Is there no help outside?
I once migrated an older owncloud instance - meanwhile it’s working flawlessly, but I also had to change a bunch by hand, it took me a few hours.
I’m especially irritated as it says “10.0.5 or later” at https://docs.nextcloud.com/server/latest/admin_manual/maintenance/migrating_owncloud.html
So I expect that also newer Versions do work.
Edit: I did the “change version in config.php”-thing:
It runs through and gives a working webinterface.
Webinterface shows what’s to do manually to fix stuff. I didn’t run into any problems so far, it’s just a bit manual work.
I upgraded from 10.8.0.4 to NC 20.0.5 and used the webupdater to 20.0.14. No problems!