syncthing has send-only and receive-only folders. You can set a receive-only folder on your backup device and send-only on your phone or whatever. With incremental backups it's not an issue. Syncthing is just the tool to get your data to the place it needs to be. Just like rsync or cp
Anyone taking backups seriously already knows the 3-2-1 rule anyway.
Syncthing frequently stops syncing on my phone and requires me to delete everything and resync. I'm using receive-only folders. I think I'm an exception but it's been a pain in the ass.
Anyone taking backups seriously already knows the 3-2-1 rule anyway.