So I’ve been having the same issue for a long time (calendar opening to September 19, 2019 even though it’s now October 2021). After reading through this whole thread I tried the suggested solution of turning off US holidays. That worked; I re-opened my calendar and it opened to today. Then I clicked on Thursday, November 25, 2021 because that’s Thanksgiving day and I wanted to see if the calendar showed that it was thanksgiving day. It did not since I had turned off US holidays calendar. I closed the calendar app and re-opened it (US holidays still turned off), and lo and behold the calendar opened to November 25, 2021, the exact date that had been open when I closed the Calendar app, not the current date. This led me to believe that whenever you make a setting change in the calendar app then your calendar starts opening to whatever date was last open when you closed the app, rather than the current day. So I did some experimenting, changing settings and then going to some random date, closing the app, then re-opening the app and sure enough each time it opens to whatever random date I was on when I closed the Calendar app. Still no permanent fix, but as far as I can tell the best solution is to make sure that you are on “today” when you close the app after making a change in settings.