Grim Dawn Multiplayer with GeForce NOW?

I recently bought Grim Dawn on Steam to scratch my ARPG itch. I’m playing it via GeForce NOW on my old laptop, and it runs fine, and is a great game.

BUT I now want to play with friends and I can’t get Grim Dawn’s multiplayer working. Because as GeForce NOW is a game streaming service there is no UPnP support and I can’t change port configurations for their servers where the game is actually running.
Thus no one seems to be able to join a hosted game and the game list for joining is always empty, too.

So: Did anybody get Grim Dawn’s multiplayer (hosting or joining) to work with the GeForce NOW game streaming service?