Vaultwarden isnt a fork because bitwarden isn’t selfhostable. Bitwarden has an official selfhosted version. Vaultwarden is a lightweight rust version of the backend. As the selfhosted version by bitwarden is quite fat. Vaultwarden uses the official webapp of the webvault in their fork.
I use syncthing to sync the sysvol folder between my two samba ad domain controllers.