Hello there! My name is Tim, i spent almost half of my 50yr life with Debian Linux and i'm stuck with this "project".

I moved my old Nextcloud server installation to a new host according to the manual from Nextcloud project [1].
It WAS running on Apache.

The new machine is running nginx 1.28.0-1+0~20250426 from Debian stable.
Two joomla domains run just fine and very fast, i'm impressed!

However, the Nextcloud instance doesn't run at all (internal server error) and it doesn't log ANYTHING ANYWHERE.

Of course i set the error_log directive to appropriate files under /var/log/nginx and raised verbosity up to debug. I deleted all log files and they were recreated on server restart, but stay empty. No entries in /var/log/syslog, journald, error.log - no matter what i do to the error_log. The log file under the Nextcloud web root is ignored just fine. File and directory permissions look alike on both systems, i copied with rsync -t.

The installation was running just fine on the old server. I didn't touch it yet, i'm running my tests on copied data.

So here i sit feeling like a schoolboy. I didn't find a switch to run nginx in foreground mode whatsoeber. What can i do?
Oh i can run php on command line just fine; executing php8.4 file.php looks very much like unformatted web site text i would like to see in the browser - however i don't. The web is filled with advice on dis- or enabling nginx logging, but it doesn't change anything. Pretty fresh install, loads of php modules like on the old server; the web root from the old server was copied 1:1 to the new, just like the database.
Only "The server encountered an internal error and was unable to complete your request."
Kindly waiting for a hint! Thanks in advance!
tim

[1] https://docs.nextcloud.com/server/stable/admin_manual/maintenance/migrating.html