“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.”
Haven’t noticed any of either during my time. At least not with any degree of frequency. Probably not something you want to be playing competitively on, if that’s what you’re into.
Lots and lots of people have reviewed them at this point with similar results.