The Steam Deck is a handheld gaming computer that runs a Linux-based operating system called SteamOS. The machine comes with SteamOS 3 (code name “holo”), which is in turn based on Arch Linux.
Although there is no SteamOS 3 installer for a generic PC (yet), it is very easy to install on a virtual machine using QEMU. This post explains how to do it.
Exactly what it says.