Create Backup from a remote FTP/SFTP to a local repository

I see in the documentation many possible destinations for a repository, but I don’t see any option to change the source of a snapshot to FTP/SFTP.

What is the best strategy to back up an external FTP to my local repository, especially considering that a full read is not always necessary due to my LTE internet connection?

I would like to avoid using Mountain Duck for the backup. I was hoping for a direct connector (instead of selecting a file) where I could set the source as a remote FTP folder instead of a local folder.

Setup:
• The FTP is mounted on three computers using Mountain Duck.
• The FTP is hosted on a managed hosting server with sufficient storage.
• I want to perform the backup on macOS, with my local router connected via mobile LTE.
• (I also have a Proxmox server, though I’m not very familiar with it yet—it could be an option.)

Source can be only local so you have to mount your ftp. I use rclone mount for this.