

Installers are just fancy zipped folder. And AFAIK, all games that are DRM free on GoG are also DRM free on Steam. So you can download the game, zip the game data folder, copy it elsewhere, unzip it and play it there. I’ve done that with several games, in fact when I was trying to convince some friends to buy a game I did that so we could play it in lan with a single copy so they would try it and buy it so we could play it online later.
So, yeah, you can absolutely do that in Steam, which is why I never get the “oh, but GoG has DRM free games” appeal.






The solution you’re looking for is to have a group that all those users belong to, and make the files have RW for that group.
The solution you should do instead is to run things inside docker, so each one gets an extra isolation layer, but all can write to the same files easily.