“There is not a native app on Steam deck today,” said Andrew Fear, GFN boss, back in January. “Use a Chromium browser to make it work. I would say that both Nvidia and Valve, I think we’re both interested in making [GeForce Now on Steam Deck] better. But we don’t have any announcements on a native app coming to Steam.”
I’ve played 100 hours of Elden Ring streaming and the difference between steam and moonlight is night and day in my experience. Steam struggled to hit 60fps streaming (definitely not the computer’s fault: it’s their streaming codecs or something) while moonlight is rock steady 60fps.