I face some issues with the caledar app, respectively caldav after upgrading:
1st problem: i realized that evolution was no longer able to connect. error message: " Data source does not support OAuth 2.0 authentication".
Temporary solution was provided by @nickvergessen in this thread: NC12 Authentication issue with Cardav, Caldav and Sogo connector.
2nd Problem: during troubleshooting it turned out that my iPhone doesn’t sync with calendar any more. No solution for that so far. Anyone with the same Problem? Any hints?