Maybe it's just me but doing a big transfer over cable is a crapshot since it will disconnect midtransfer. KDE connect is a bit better but syncthing is the best solution still.
Doesn't MTP require plugging in a USB cable? KDE Connect works wirelessly as long as your phone and computer are on the same network.
KDE Connect just uses an SFTP file mount. You can do that on any system that you can ssh.
But I wouldn't use that for backups, I'd use rsync.