I have a quite similar issue as my previous poster.
But I had Nextcloud running for quite some time now. This error just suddenly appeared (maybe with last Docker update?).
Unfortunately I cannot rollback to a backup since my backup-settings were wrong and I have only one backup from "not working state".
Please, help?
Thanks in advance!
(sry for bad english)
Edit:
I ended up reinstalling Nextcloud and MariaDB, now it's working again