It seems the game isn't compatible with my ARM Mac. Not surprised, but should be updated on the store page and Galaxy page to indicate system requirements.

While you're there GOG folks, I hope soon there will be information in Galaxy itself, to show which games are Mac 32 bit only, so I don't have to check the store page for each one. All the mac games will allow themselves to be installed but obviously not all (not many) are working on recent Macs

Been trying to get Bootcamp going again on one of my old Mac Pros, but that's another story