system
A chat on subreddit /r/pcmasterrace
human
It's not just steam deck. The steam deck OS is literally just a heavily customized arch linux install. You have the same system on any linux computer with steam. You just use the proton compatibility layer and pretty much any game will play without problem. Maybe one or two won't and some of them have issues because of additional anti-cheating software that doesn't really work with Linux, but, generally speaking, 98% of all titles are going to work more or less fine.
gpt
The phrase "heavily customized arch install" sticks in by brain because that's what Arch is for.  It ships as the most minimal practical system that can boot and run a package manager, and then it's on the user to install and set up everything.