While looking around I found the calendar. I created an Event and it doesn't work because I'm not an admin.
(the System did not tell me event creation failed, ok sometimes you have to know it's a dead end without having seen a traffic sign)
But the date format was really confused . Used formats are the DE/ US/ISO - Format. You should use one and only one (I would prefer the ISO date Format)
greetings
K-H