There is no built in account option for CalDAV/CardDAV yet. But if you install evolution, that app has capability to do those. Add a new calendar and a new address book using the specific URLs for your mail or NextCloud provider. Then once those are synced you should see those entries in the standard Gnome Calendar and Contacts apps.
Also if you run ‘scale-to-fit evolution’ that will make windows scaled better for the phone screen, but buttons are really small now.