2100 Games On The Steam Deck, with Metro 2033 Redux and Resonance of Fate as Verified - Boiling Steam
boilingsteam.com
A new milestone for the Steam Deck, with 2000 games validated (playable and verified) now available on the first of April 2022

The real number is probably much higher. I routinely play games on my Arch laptop that are neither verified nor marked as playable.