From my understanding Steam Decks come with SteamOS preinstalled on them. Yet when you look at the list of games on steam that are compatible with Linux + SteamOS, its a small fraction.
But what confuses me is this page
https://store.steampowered.com/steamdeck/mygames
It shows your games that are compatible with the Steam Deck which has a Linux based OS. And almost my entire library is compatible with the Deck. Can someone help me understand how this is possible? If games are compatible with the Steam Deck, why wouldn’t they also work on Ubuntu for example?
“Linux + SteamOS” compatibility is a bit legacy. It mostly refers to games that have a native linux client (I believe some of the early Proton Validated games are included as well.
The Steamdeck (and generally speaking, any linux system) uses Proton as a compatibility layer with windows, and the “Steamdeck Verified” system is more relevant today. That said, even the Steamdeck verified system isn’t perfect. There are a number of titles that, while verified, have some problems with the deck, typically later in the game or after running for some number of hours. There’s also a vast number of games that while not “Steamdeck Verified” work perfectly on the deck and linux via proton (though you do have to enable it in the settings).