don't even need that much... just SSH + Files.

On server:

    mkdir -p ~/repos/foo.git
    cd ~/repos/foo.git
    git --bare init

On desktop:

    git remote add backup ssh://user@server/~/repos/foo.git
    git push --all backup

Or something similar, been a while. Can use an absolute path too if sharing, need that path setup for +rwx for user/group. Used to do this as a quick and dirty remote for git usage. You can also setup a git user and add your public key, but find that isn't really necessary.

edit: looked up commands, made a couple minor tweaks.

note: this doesn't include any kind of LFS support if you're needing it, consider a more complete install, unsure on gitea or gitlab etc.