I got a calendar notification of a cancelled event. The notification itself had no buttons to interact with. A hover where the close button would be (top left of the nmotification) causes it to appear and also causes a "delete" button to appear in the bottom right. But if I move my mouse off the "close" button to click "delete" both the close and delete buttons disappear. The only way to delete it is to click it (opening the calendar) wait for the calendar to open (5-10s on a 2019 i7 MBP) then open the event itself to delete it.