Since some versions the file retention feature does no longer work. There are issues on github reported in Dec 2020!
→ Error: Call to a member function getUID() on null since use of files_retention 1.9.0 · Issue #128 · nextcloud/files_retention · GitHub
So please give hints what patch is needed to solve those probs.
File retention is a very important feature and should have a high prio.
Thanks a lot.