Getting "Update needed" after trying to restore from backup (21.0.1 > 21.0.0)

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Nextcloud version (eg, 20.0.5): 21.0.0 / 21.0.1
Operating system and version (eg, Ubuntu 20.04): Ubuntu 20.04.2 LTS
Apache or nginx version (eg, Apache 2.4.25): 2.4.41
PHP version (eg, 7.4): 7.4.3
Database: PostgreSQL

Situation:
Upgraded Nextcloud from 21.0.0 to 21.0.1 and ran into this bug (Fatal: `Sabre\DAV\Exception` Could not rename part file to final file · Issue #1453 · nextcloud/groupfolders · GitHub) with group folders after the update, which prevents users, who have subsets of group folders shared with them, from uploading into these shares. Waited some time for a fix, then decided to restore the VM snapshot from before the upgrade, which worked fine. Since a lot of data has been added after the upgrade, I wanted to transfer it to the restored instance.

What I did:
As per these guides within the Nextcloud documentation

/admin_manual/maintenance/backup.html
/stable/admin_manual/maintenance/restore.html
/maintenance/migrating.html

I deleted all contents of the 21.0.0 data folder and transfered the whole content of the 21.0.1 data folder into it. I dropped the Postgres DB and created it new. I then restored the 21.0.1 DB dump into the 21.0.0 DB.
Regarding the DB I ran into the problem that using the command
PGPASSWORD="password" psql -h [server] -U [username] -d template1 -c "CREATE DATABASE \"nextcloud\";"
produced a permission denied error, while the db drop worked just fine. I fixed it by
sudo -u postgres psql
into the db and creating the db by hand for the old db user. Restoring the db dump by using
PGPASSWORD="password" psql -h [server] -U [username] -d nextcloud -f nextcloud-sqlbkp.bak
then worked fine. I do however have the problem, that when I now try to use adminer to log into the db I get FATAL: Peer Authentication Failed For User.
As for the Nextcloud, when I take the 21.0.0 out of maintenance, I get the Update needed message in CLI and on the web interface as well.

Any ideas what I could do to fix it? Just restoring the old VM and loosing all new data would be a major pain… Thank you so much! :slight_smile: