As noted in an article on PC Gamer, Valve's upcoming Steam Deck portable PC may have a problem when it comes to some of the most popular games around. Due to being a Linux-based system, titles such as Apex Legends, Destiny, PUBG, and Rainbow Six Siege will not be playable on the device out of the box. Since Linux is incompatible with certain anti-cheat implementations featured in these games, SteamOS' Proton compatibility layer simply cannot get past the anti-cheat check required to boot each title.
While Valve has stated that it will be updating SteamOS to potentially circumvent these issues (even noting that it will be working directly with different vendors to ensure compatibility), there is one really nice feature that the Steam Deck has: owners will be able to reformat the device at will. Natively speaking, Steam Deck cannot run these games, but an install of Windows will let you bypass any issues that SteamOS might have.
There's obviously the caveat that Valve hasn't validated the Steam Deck for usage with a Windows install. The rated battery life and theoretical performance may not be the same under those conditions, which could affect how the aforementioned games run. All of them can basically run on toasters at this point (save for Destiny 2 which is a much more modern title than the others), but if you're only able to play for an hour with Windows on battery, then it's a really awful trade-off.
That said, the modability of the Steam Deck will be the biggest strength of the device. Users won't be able to tinker with the hardware configuration all that much, but the ability to swap out storage and install different operating systems on the system will open up a ton of opportunities for playing games. The only thing that will really stop widespread adoption of the system is that most users do not know how to use Linux. That and the hardware may not last a full generation (it does seem relatively underpowered), but we'll just have to see how well optimized SteamOS is before jumping to any conclusions.
Source: PC Gamer