Yeah, when I made the switch, I checked a bunch of the games I played the most for steam deck compatibility and thought I had to give up on some of them, only to find that they were still fine because my desktop is much more powerful than the steam deck. Plus it has a keyboard; if a game requires a keyboard, it hurts the steam deck compatability score (how much depends on if it's required for playing the game at all or just needed every now and then to enter some text).

So treat "steam deck supported" as "works on linux" and "steam deck unsupported" as "maybe works on linux".

I think the better indicator of not supported at all on Linux is the "3rd party kernel anticheat" marker in the store, though I tend to avoid games with that anyways, so I can't really say for sure.