Files and Calendar does not work anymore

Running NC 22.2.3 on a Debian Server.

I wanted to get rid of the midnight notifications of the birthday calendar. In a forum I read the workaround to switch off and back on “Automatically generate birthday calendar” in the admin panel.
So I did then, but since then both Calendar and Files do not work anymore.

When accessing Files in the browser, it says:
“This directory is unavailabe, please check the logs or contact the administrator.”

The Calendar page keeps loading, but doesn’t display any calendar.

Desktop app tells me:
“No connection to Nextcloud at Server replied: “500 Internal Server Error” to “PROFIND” (syntax error, unexpected ‘public’ (T_PUBLIC))”

Running occ maintenance:repair tells:

And log files tell me:

Any ideas how to fix this problem?