Headless client as a daemon

There are more scenacios where it's needed but this is mine:
I have a LAN with a CLI-only server and multiple Desktop computers. Client computers have a sshfs mounted point to a common directory on server (this is SFTP/SSH). All in sync and it just works as a shared folder.

I also use a notebook to connect to that shared folder from Internet, but Internet connection sometimes is poor and I can't wait all the time for folder refreshes and files load/save in sync.
Solution seems to be Nextcloud (server at files server to sync with a real folder, and desktop client at roaming notebook).

I'm looking to nextcloud-desktop-cmd (to replicate in server as a bridge between real folder and Nextcloud server storage) and it does not satisfy all my needs because it should:

- Start as a SystemV/Systemd daemon without user session.
- Do not depend on desktop software, to be lightwheight same as OpenSSH is for a light server.
- Allow to specify local user:group and umask for new files and directories.
- Allow to setup more than one WebDAV client account with all data (local path, remote URL, username, password, local owner:group, local umask, etc.)