hmm interesting idea. I do not get the idea that nextcloud is reliably "easy" as it's kind of a joke how complex it can be.
Someone else suggested WebDAV which I believe is the filesharing Nextcloud uses. Does Nextcloud add anything relevant above what's available from just WebDAV?

This is my fear! I have done it before.... Forgetting something is synced and deleting what I thought was "an extra copy" only to realize later that it propagated to the original.