You can't make the client untrusted to the point of "I don't trust that the human really pushed the button" or you don't have a useful multiplayer mode anymore. Cheaters are truly ruining everything, here.
Like so many seemingly intractable moderation problems maybe this is why we shouldn't scale to infinity. YouTube is literally too big to moderate. Maybe this is a feature of humanity. What's wrong with more, smaller communities that have a dang to keep everyone in line? Other than the unfortunate lack of dangs in the world.
Back in my day CS servers were mostly privately run. If you were caught cheating you got banned. If you appeared to be cheating (you were too good) you also got banned. From the perspective of the players on the server those are the same thing. Communities formed on servers with similar skill levels and recognized players. Cheating in that kind of environment becomes extremely risky from a social perspective. You could piss off your actual friends.
There wasn't a need for rank-based matchmaking or anti-cheat or anything like that, you just eventually found a place you fit in and could have fun. Valve tried to replace that with algorithms but maybe they should "crowd source" so to speak, like we did 20 years ago.
This is all a lot of words to say that there is a "right size" for a community to form and enable everyone to have a good time. When you get to the point that "technology can't help us" I think that's an indicator that your community is too big.
They're doing that too.
Fortunately, most cheaters don't know how or are not trying that hard to hide, and are identified by pattern recognition. It's not that big a problem in practice. It's still universally considered cheating.