> there's apparently a checkbox to enable Linux support on EasyAntiCheat - and some don't "check" it

Because support doesn't mean full features. It's like saying iPad supports Microsoft Excel. At some point it's the same name for different software.

I think especially because it's under Proton, that means it's the Windows version of the game you're weakening to anti-cheat too. Even Valve's own VAC has issues running under Proton.