System.InvalidOperationException: There is an error in XML document (0, 0).

[da9]

After some experimentation, I could get it working by deleting migration.xml and system.xml.

If one would like to fix this problem too, he can try deleting only these so that configs aren't lost unnecessarily.

Thanks a lot, this worked for me too. I simply moved these two .xml files to another folder (for backup purposes). Restarting the docker cluster afterwards re-created the two files and booted Jellyfin properly.