They probably gave up on preventing cheat entirely, and are just trying to reduce the amount of cheaters by making cheating as annoying as possible.

I do actually believe them when they say that cheating on Linux can be made significantly easier and more comfortable than on Windows. I think it’s a real fundamental issue for Linux, multiplayer games with toxic playerbases can be unplayable due to users being able to do what they want. They would have to make systems to allow for playing in smaller human-moderated servers, or rely purely server-side solutions

It’s not proton that is exploited. It’s the kernel itself that cannot be monitored by anti-cheats, meaning cheaters could install a modified kernel to mess with the anti-cheat