GNOME supports CalDAV and CardDAV, unfortunately it isn’t exposed in the Accounts settings. You would have to use Evolution to add Contacts and Calendars. After that they appear all the apps which are using GOA (GNOME Online Accounts) like the default calendar and contacts app. Yes, an option to add them in the Acounts pane without using Evolution would be nice.
Wireguard shouldn’t be a problem either. It has landed in Linux 5.6 and I guess it doesn’t take too many time to support it in the VPN settings for GNOME.
Edit: Concerning WebDAV: Nautilus, the default GNOME file manager, supports WebDAV. When it has finally been ported to mobile, you can use it like any other external file storage directly within the file manager.