It was removed upstream in https://github.com/syncthing/syncthing/pull/9611 and the stub generated by nixos now prints an error in the logs due to it not having a ExecStart line.
It was removed upstream in https://github.com/syncthing/syncthing/pull/9611 and the stub generated by nixos now prints an error in the logs due to it not having a ExecStart line.