As a publisher: Yes, Epic stopped the Rocket League devs from continuing to build Linux binaries. To my knowledge, they have not disabled "support" for Proton in any of the anti-cheat solutions.

Similarly, the development branch of CD Projekt (the parent company of GoG), apparently had Linux binaries for The Witcher 2. They do not for The Witcher 3 or Cyberpunk.

Both companies decided it was not worth internally supporting Linux and instead rely on Proton/Wine to do it for them. Whether that is good for gaming is debatable, but both are "actively hostile towards Linux" in that regard.

If you do want to criticize the handling of Linux then I would suggest looking into the Unreal Engine marketplace (or whatever they call it now) being a complete shitshow for Linux developers. Which is ironic since the UE documentation is actually great for Linux devs. I cannot speak to the CDPR efforts with their modding SDKs since I haven't opened one since The Witcher 1 (when it was either a hacked version of the NWN toolkit or an officially hacked version of the NWN toolkit).

But that is Epic and CDP not EGS and GoG.