I mean, Valve could explicitly say that they have some trusted hardware and software stack or something and let games know whether the environment's been modified.

That'd require support from Valve and be about the only way that you could have both a way to run in locked down mode for multiplayer games where addressing cheating is a problem (and where I think the "closed console system" model is probably mote appropriate and the "open PC model" is at best kludged into kimda-sorta working like a console) and also let the system still run in an "open mode".

My own approach is just to not play most multiplayer competitive games on PCs. I've enjoyed them in the past, but for anything seriously reflex-oriented like FPSes, your reflexes go downhill with age anyway. And they come with all kinds of issues, even on a locked-down system that successfully avoids cheating. People griefing. You can't generally pause the game to use the toilet, deal with a screaming kid, or answer the door. The other players, unlike game AIs, aren't necessarily going to be optimized to play a "fun" game for me. You don't need an Internet connection, and being in a remote area isn't a limiting factor.

I think that the future is gonna be shifting towards better game AIs. Hard technical problems to solve there, but it's a ratchet

we only get better over time.