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?