iirc Easy-Anticheat has a sort of “Lite” mode that also runs on Linux, enabling it makes the games work with Proton but iirc degrades the Anticheat capabilities on those Systems. Because the Linux Anticheat isn’t as effective (and because it’s an Opt-In) most games don’t use it.

Talking a lot out of my ass here but I think that’s how it was explained back when they made that change.