Prerequisites are supposed to be either part of the Steam Runtime package that comes with Steam for Linux, or installed as part of a given distribution's rollup of native replacements for the Steam Runtime.
Could you, perhaps, list any applicable game titles, and the prerequisites that aren't met? This probably also depends on your distribution, and how you installed Steam.
I'm thinking they're implying driver/mesa/esync/llvm requirements. Showing it in client when you run a proton powered game.
https://github.com/ValveSoftware/Proton/blob/0c7144c32cefe4815951f2b9eb899bb16147f123/PREREQS.md
Oh, that would definitely be useful.
Nothing extracted yet.
Proton should be triggering a warning when prerequisites are not meet. The warning should be optional. Currently, it's a little difficult to know about prerequisites.