I’ve used both syncthing and recently resilio. My Syno NAS has their own app Synology drive. All three have worked great for me.

Syno ds920+ w/2 16’s & 2 6’s. Use: home docs, pics, and a Plex server.

QNAP ts233 with 2 6tb for “off-site” backup sitting on my desk at work connected to the guest wifi backing up the home docs and pics from the syno.

Syno 920+ for me