I've got it running 6 person server running on steam deck. in fact im about to host right now for the stream session they are doing. I did learn i have to run it from Desktop mode as you said. i ran it from a different steam-account who doesn't own the game, but is in the family network. Thankfully it has a different app-id so this works well. the point im at now, is trying to see if i can run it as steam CMD or as yet a -third- user, so i can run -both- my 7d2d servers from the steam deck. as we have the Stream-server save i host. and my family-friends save i also host. once i started hosting from the steam deck, my friends said its running the smoothest and least laggy they've ever seen! so im very pleased the steam deck is out preforming my windows pc (which isn't too shabby but still doesn't have ddr5 memory like steam deck).