I'm now using radicale for calendar and contacts. This was very easy to install and configure in manjaro linux. I'm using this in conjunction with radicale-imap plugin for authentication. Eventually I might look at an SSO solution for the variety of services I have installed on my server.
Google supports exporting contacts in vcard format, and calendar events in ics format, both of which can be imported in a capable calendar or contacts app in android.
Radicale depends on python, which is OK but possibly more susceptible to python environment changes than I would prefer. I had looked at fennel server which is implemented in golang, but as yet this isn't compatible with Dav5X on Android due to incomplete implementation.