In case you don't own a Steam Deck and would like to see how much of your library would run on Linux:
1. Go to your library
2. Click the filter button
3. Under "hardware support" you'll see a dropdown "Steam Deck" with 4 options, here's some explanation what they mean:
Verified - Means this game 100% works on Linux (and Deck), which is verified by Valve
Playable - Means this game works on Linux (and Deck) but it might have some tiny issues (e.g. font size)
Untested - Might work, but not tested
So to check if your games would run pretty nicely either filter on "Verified" games or "Verified or playable" games and it filters out everything which will or might not run at all.
You'll be surprised how much games can run on Linux these days -- thanks to the massive effort Valve puts in Proton and some devs (including Valve) publishing native Linux builds of their games on Steam, and even things you might not even consider at all like Skyrim or Oblivion with all your favorite mods (!)