I can recommend Restic over Rclone over SSH for limited, append-only access.
Specifically, you can force the Rclone command on the server using SSH's authorized_keys file like so: restrict,command="/usr/local/bin/rclone --config /dev/null serve restic --stdio --append-only /var/restic/alex" ssh-ed25519 ... To be used as follows: restic --repo rclone: --option rclone.program="ssh restic forced-command" ... Alternatively, you can use the Restic REST Server to achieve more or less the same thing over HTTPS: https://github.com/restic/rest-server
