Seems pretty clear to me: “We’re also releasing Civilization VII for MacOS and Linux / SteamOS” doesn’t just not mention Proton, there also isn’t a Proton on MacOS Steam. And you don’t get Linux and Mac system sepcs and platform icons on Windows-only games on Steam whether or not you can run them with Proton; you get ”Steam Deck Verified”.
(I’m half expecting them to walk that back later but for now the message seems clear.)
I dunno. There’s no Proton on Mac, so lumping Mac and Linux together when they really just mean Proton wouldn’t make much sense. There are native Mac and Linux games on Steam, and the Steam store page has icons and system requirement tabs for all three OSes, neither of which happens with Windows-only games. “We’re also releasing Civilization VII for MacOS and Linux / SteamOS” also sounds like they’re talking about actual Linux and Mac builds. It could all be miscommunication, of course. That wouldn’t surprise me.