Valve Can Bring More Users to GNU/Linux, But It Won't Bring Freedom
Steam is DRM, it's proprietary software that brings more proprietary software (or games) to your computer. SteamOS is Arch Linux with Steam preloaded; in different terms - more generic terms - it's a platform for DRM. It's otherwise just some Arch Linux with particular optimisations.
The number of "gamers" who use GNU/Linux is growing. They don't choose GNU/Linux because they want freedom, many just happen to purchase a gadget called Steam Deck. It boots GNU/Linux and then starts all the "DRM stuff" on top of it. In some cases, people use Steam on top of GNU/Linux for a PC. Valve does not quite distinguish; SteamOS can be installed on devices other than a "Deck" and a "Deck" can take another distro of GNU/Linux.
While it's better that "gamers" do not use Windows as much as they used to, there's danger that they will bring with them rootkits and other 'Digital Gulags' like 'Secure [sic] Boot', as Andy has put it. █