“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.”
On a browser, the max resolution is 1080p and max framerate is 60fps. It is also significantly less smooth and a bit laggy when compared to the native client. The difference is huge.