For sure I run into a nextcloud server side bug again.
I deleted over the last year a lot of things in my nextcloud account as well as other users, which are running in the same instance.
One day, I looked into my Trash(Deleted files) and it was empty:
That is not real and not possible, I thought.
Tried to find a solution or at leased a bug report on the github nextcloud-repository-issue-tracker, I found many, and it seems like this issue comes from time-to-time again into new nextcloud releases.
In my case probable since the update to nextcloud version 16.0.3.
The solution is very simple delete all user trashes from the command line:
sudo -u www-data php occ trashbin:cleanup --all-users
And this magic freed 49GB of space on the instance, where nextcloud is running.
Maybe someone has a more efficient and less destructive solution for this one issue? Let me know :-)