Apple Watch has stopped syncing Calendar

Since last week my Calendar has stopped synching to my iWatch. Until then it worked flawlessly.

I am using the built-in Calendar in iPhone and neither my iCloud nor Outlook Calendar items are synching. All old Calendar items are visible but not the new.

Anyone who knows what I can do? I have stopped the synch and started it again and I have also turned off my iWatch and turned it on again.

(iOS 18.0.1, watchOS 11.0.1)

[Re-Titled by Moderator]