There are both software and hardware components of Steam offerings, and it's easy to get confused because of them.
SteamOS was created originally for the Steam Deck handheld gaming system that's available now. Suitability for general-purpose PCs is iffy because it's specifically designed for Steam hardware and support for non-standard peripherals may be spotty. Bazzite was created (IMO) as a more-conventional Linux distribution that maintained many of the features of SteamOS. Based on the reviews I saw, SteamOS has a gaming mode as default but also a desktop mode that looks like bog-standard KDE.
Keep in mind that Steam itself is just an app, or rather a mini-ecosystem of apps, that should technically be installable on most modern Linux distributions if the PC hardware has enough strength to run it. I ran it on Fedora semi-successfully; most of the apps in my Steam library worked well, but one of my games is documented not to run and another was claimed to work but didn't.
Underlying all this is Proton, the layer that replaced Wine that is installed with Steam, which allows Windows games to run under Linux without requiring (much) involvement of the game developer. The
ProtonDB website carries a fairly comprehensive list of Steam games and lists their compatibility with the Steam Deck (and thus Linux in general). An impressively high number of Steam-offered games will work, but notably. multiplayer games that include some form of anti-cheat mechanism are almost guaranteed NOT to work. I am told that non-Steam catalogs are supported but can't verify.
The Steam footprint in this world is going to get even bigger because of the November announcement of the Steam Frame and Steam Machine to be released early in 2026. A good reception for these products will be good news for Linux and for Linux gamers, even those not using Steam hardware.