Currently, there are 2,988 Steam games listed as "verified" and 5,032 listed as "playable". As caught by Overclock3d.net, this is a total of 8,020 games, and way more games than Sony PS4, which stands at 3,282.
There are a couple of big titles that have been recently added to the Steam Deck list, which include Atomic Heart, Cyberpunk 2077, Resident Evil 3, and others. The most played games for February include, unsurprisingly, Hogwarts Legacy, Elden Ring, Red Dead Redemption 2, and The Witcher 3: The Wild Hunt.
Of course bear in mind that these 8,000 games only include titles available on Steam, while it can also play games via other PC games stores like Epic Games Store, GOG, Ubisoft Connect, and EA App.