

In a web browser I use the NextCloud one. It’s functionally very similar to Google and I like it a lot.
For our Android phones, my wife uses the Google Calendar app, and I like Business Calendar Pro.
Both apps you just have to go into the settings once DAVx5 has done the initial sync and uncheck all of the Google calendars so they aren’t shown, and check the boxes next to the new Calendars.
Exporting and Importing I could only really easily do via the web browser for both.
The Google account is still there, I’ve just hidden each of those calendars. New events seem to default to whichever calendar you used last (citation needed) so once you’ve created an event under the NextCloud account, it should default to that. The app I use (Business Calendar Pro) doesn’t even give the option if a particular calendar is disabled.
As far as DAVx5, the default is to only sync every 4 hours. Phone to NC is instant (once DAVx sees the change), but NC to Phone has a delay. However!..
I just set up the ntfy app to create instant two way sync both ways. It’s pretty slick. Dig around in the DAVx5 documentation about how that works. You install the DAV Push app on the NC server, ntfy on your phone, enable UnifiedPush in the DAVx settings, do a little dance, and then NC notifies DAVx every time there’s a change.
Edit: you can also delete calendars from Google Calendar settings on the web, but this is obviously permanent. I think you can also totally remove Calendar from your account.
Edit2: You can’t remove calendar from your account, only delete individual calendars.