Events don’t display backend

Hi team,

Events are not being displayed backend.
Frontend and in the MySQL-database tables all events are present and can be seen.

I can add new events and this is visible in the backend interface.
Existing events don’t display and therefore cannot be altered.

I tried:
– safe mode Divi theme
– change PHP 8.0 < > 8.1 < > 8.2 back and forth.
– deactivated all plugins
– use standard WordPress theme

How can I solve this?
Thanks for any help,

E.