"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."
Been using Xbox GamePass w/ GeForce Now for a while and can't see why anyone wouldn't like it. For $30/mo I can play on any device, anywhere with a decent internet connection. It uses almost no power, so my batteries last forever. I get the best gaming experience available on my gaming monitor without spending thousands on hardware that sits totally unused for 99% of the day. My room does not heat up to 100*F. I get access to a wide variety of top-tier games for a minimal fee. It's pretty great.