Upgrade 19 -> 20 breaks everything

Nextcloud version (eg, 20.0.5):
Operating system and version (eg, Ubuntu 20.04): docker
Apache or nginx version (eg, Apache 2.4.25): apache from docker
PHP version (eg, 7.4): php from docker

The issue you are facing:

After upgrade I can no longer log in. nextcloud.log contains several mentions of:

Can not decrypt this file, probably this is a shared file. Please ask the file owner to reshare the file with you.

Is this the first time you’ve seen this error? Y

Steps to replicate it:

  1. I was running nextcloud 19 from docker fine
  2. upgraded to nextcloud 20 from docker
  3. ran occ upgrade
  4. can no longer log in