Thank you @face for this great tipp! I’m on Qubes 4.2 too and this is so much more convenient than figuring out the involved port forwarding described in the docs.
Performance, which is the disadvantage of this simple method, seems pretty decent for my simple use case of syncing large files with syncthing. I get ~40MB/s on a Gigabit network with the host being a i7-7820HQ serving from a HDD.