Apple watch calendar not syncing

I am using an Apple Watch Ultra 2 using the latest version watchOS 11.5

The calendar is not syncing.

I have:

1. switched on and off calendars (instead of just mirroring)
2. switched on off the apple watch
3. changed the apple watch screen (which helped earlier with the same kind of problems)
4. tried reset sync data (which does nothing at all)
5. reset the complete watch

This all did not help. Any other ideas?

I am using the calendar app of apple with apple calendars and one outlook calendar. It did not change switching off the outlook calendar either.