I use davx5 (F-droid) and nextcloud (self hosted) for calendar and contacts. Nextcloud can be run on a raspberry pi or similar. Some rpi distros have nextcloud as a one-click install (like nostr:nprofile1qqsw5t3us9xs3gmclzjm37hvk2yy6pv9t96utjjttsj794hexc5x79qpy9mhxue69uhhyetvv9ujumr90p5kuem5dahxy6t5vdhkjm3wdaexwtcahy3z8.) I dont want google harvesting that data. You can share calendars with other users on your nextcloud through the web interface.