Actually, FYI, you can do that for a large percentage of Steam games, maybe even most, if you use the Goldberg Emulator that replaces the steamapi DLL.

Steam DRM is one of the easiest to bypass around, and I like to think that’s very much a purposeful choice.

However, the entire thing is designed for it not to be easy to do for somebody with the technical know-how of the average gamer, plus it’s not reliably possible and there’s no way to know upfront if it will work or not when making a purchasing decision on a game in Steam.

Meanwhile “No DRM and with downloadable Offline Installers” is literally the Unique Value Proposition of GOG as a games store - access to download offline installers is there in the games page after purchase and that installer is guaranteed to work forever and ever if you still have the hardware and OS version supported by the game.