

Supposedly so long as it’s the Epic Online (EOL) version of EAC, then it’s about as easy as checking a tick box in the settings.
Any developer who cares enough to enable it would most likely test that it works as expected and make a couple of tweaks before announcing the support. It’s usually not a good idea to take a vendor by their word that it “just works”.
This doesn’t affect valve at all though. It’s borrowing their tech that they’ve made open source, and figuring out how to use it elsewhere outside of steam.
Actually, it’ll benefit them. More eyes are on proton and any fix will benefit everyone, including games played via steam.