Really I'm surprised nobody's done "WinBox" yet. Proton kinda covers that except it runs in Linux, not Windows. I dunno how it handles old Windows games as I've got zero nostalgia for those, my Steam Deck mostly runs modern stuff from small teams.
The things GOG is improving are some bugs that occur mostly in games, e.g. something with color palettes in pre-2002 games. But I think every game using DirectX 9 or later will work without any adaptations, even ten years from now.