If there's always at least one computer switched on (which be a rented VM, or even a phone if that's enough storage) then Syncthing could work. I haven't tried

If there's always at least one computer switched on (which be a rented VM, or even a phone if that's enough storage) then Syncthing could work. I haven't tried making many edits from different places with lots of time offline though — mostly, I use it to sync photos I take on my phone to my computers and vice-versa for DSLR pictures, and music etc from the computers to my phone. Files generally sync within a few seconds. rclone is the cloud equivalent of rsync, it syncs to S3, GCS etc. But you'd have to set up the "latest version" part yourself (--update?) and something to make the synchronization happen after changes (inotify on Linux?).