Does not work anymore, Apple decided to change the URL, in particular, the PROPFIND looks like so now:
for whatever reason. In the past, it was
So we need to remove /inbox/
RedirectMatch temp ^/remote.php/caldav/calendars/(.*)/inbox/ https://<your_server>/remote.php/caldav/calendars/$1/
And Calendar.app is happy again 🙂
You may substitute temp with permanent after testing.