While many are excited for the Steam Deck to come out, the hand-held PC may have some issues preventing certain games from being played. To be more specific, the anti-cheat system which games like PUBG and others use will cause issues with the Stean Deck and prevent the games from playing online.
Valve has said it is working to improve Proton and the Steam OS and correct the issue but has not said how it will address the issue. While the company has a few months to solve the issue, MMOs and other competitive online games that should be killer apps may be left out when it comes to the system.
The Steam Deck is tentatively launching in December 2021.