Actually, I think that might be harder than you'd imagine, at least as things work right now

Valve would probably need something in the Proton API to help ensure programs don't think each version is a different PC as that is kinda the point of how Wine/Proton work (by creating a fake virtual PC and running things through that), or change how prefixes are handled so that all proton versions default to the same prefix (which would have other issues im sure)

None of which would be a problem if they just exported the game from their software into a native Linux format, of course. Doom runs on Unreal, yeah? Should take 0 effort to make a native Linux version of the game, but they won't

Denuvo's whole schtick is that your unique system environment gets used as a part of the "unlocking key" of sorts, so it would definitely not be simple. For example windows users face the same issue with denuvo whenever windows updates, although obviously that doesn't happen often enough to be an actual issue.