Linux is currently able to run 80 percent of top 100 Steam games thanks to Proton compatibility, and it means that Steam Deck will be able to do the same. Currently 80 percent of games for Windows are ranked “Gold”, meaning a little tweaking here and there will let the games be smooth. If no tweaks are required at all, game will then be ranked “Platinum”. So you see the difference easily here.
The thing here is that most of the big hits are still not available due to various issues. The list includes titles like Halo Infinite, Apex Legends, Destiny 2, New World and PUBG. One of the biggest reasons for this is the anti-cheat engines used for those games. With such games out of the race, Steam Deck may actually lose the appeal it had for many gamers. We are yet to see how Steam will deal with this, but it is also still early to jump to any conclusion, thus we would suggest on staying hopeful and patient for at least until the end of next year as device is still pretty fresh.