That’s on me. I keep forgetting you’re not using a Linux filesystem on that storage device so chmod doesn’t apply here.

In your case I’d put a # in front of the option user 'syncthing' line in that conf, then check your paths in Syncthing GUI → Settings → Actions → Default Configuration → [ Edit Folder Defaults ] . You’ll need to restart Syncthing (Syncthing GUI → Actions → Restart).

There’s also a log in Syncthing that may be helpful for info under Actions.