Like this?

I have my books on a remote share managed with a local calibre install on my desktop for easy transfer

Just set up a Joplin cloud server for me and my buddy to do a writing project. It’s the most robust open source solution I could find for the situation and so far it is meeting every expectation.

You could use a different service like one cloud or google and encrypt your data. Or you could get a pi, run it as a mini server, and run any number of docker containers from joplin cloud to nextcloud, or a simple webdav server.