Fastmail (caldav) calendar

I’m a new Budgie user (loving it BTW!) and am trying to setup my Fastmail calendar in the Calendar app. Fastmail uses CalDav, so I go to Manage Calendars > Add Calendar… and enter the CalDav URL and other details. It does a loading thing for quite a while before finally popping up with a login screen. I enter my username and password and the calendar is added (I’ll refer to this as the FM calendar). Then another (different) login screen pops up and asks for the username and password of an ‘On the web’ calendar. I enter the same login here and then there’s another calendar added (I’ll refer to this as the OTW calendar).

The FM calendar doesn’t show any events, but events can be added to it. While the OTW calendar shows all my Fastmail calendar events, but no new events can be added to it.

It seems that the first calendar I setup (FM) is a local, non-synchronised one, while the automatically-created OTW calendar is the Fastmail synchronised one but is read-only…

I read in Calendar CalDav Support that Evolution is needed to properly use the calendar, so I installed that, then repeated all of the above, but with the same result.
Can anyone help me work out what I’m doing wrong?

So it turns out that you need to add calendars via Evolution, and then they’ll appear in the Calendar app as well. So that all works now.

However the problem now is that, even though I have set Calendar as the default calendar app (not Evolution), Evolution still opens when I click on the time in the top panel and select ‘Calendar’. Is there a way to make it open Calendar instead of Evolution?