Class Team calendar doesn't show in the class startpage

I used to love the startpage app in class teams, but since the spring of 2025, the calendar is not imported to show in the startpage under teaching schedule. If I add a calendar to each class, it doesn't show either. The teaching schedule says the group doesn't exist any longer, maybe it has been deleted (no it has not been deleted). All I seem to be able to. The only way is by is to make all classes to M365 groups, but that shouldn't be necessary, or is it? Sad to lose the generel calendar in class teams. Thanks for any help or advise.