Valve's Steam Deck handheld gaming device may not be able to play all titles from the Steam library like Valve promised, due to compatibility issues with anti-cheat services. The ProtonDB compatibility layer SteamOS 3.0 uses, which is the Steam Deck's operating system (OS), is currently not compatible with any games supporting anti-cheat services.
ProtonDB is a compatibility layer for Linux that is designed to make Windows games in the Steam library fully compatible with Linux in a seamless matter. Because SteamOS uses the Linux kernel, it also works with ProtonDB to get Windows games to function within the OS.
However, ProtonDB is still in its infancy, and Valve is constantly growing the number of games it supports and features required to support specific games.
So if Valve can't get anti-cheat services to work, this could turn into a major problem for owners of the new Steam Deck, as nearly half of Steam's most popular games, including Apex Legends, Destiny and PUBG, feature anti-cheat services to keep hackers at bay.
On the bright side, Valve has stated they it is accelerating ProtonDB's game compatibility for Steam Deck specifically and working on supporting anti-cheat solutions. However, there is no guarantee Steam Deck will support all anti-cheat services on all games from the Steam library.
There is always the option to install Windows 10 (or Windows 11) on your Steam Deck if the issue becomes unbearable, but that would be an annoying workaround at best.
Hopefully, Valve will get around this problem once the Steam Deck goes on sale in December.