You also dont own your individual copy, just like with any other installer you merely have the license to use it which can be revoked anytime.

You usually have to copy the game folder, but it varies a bit between games. FYI pretty much any game that’s aviable on GOG is DRM free on steam too.

You can just copy the installer and send it to them, so functionally it works. What you can’t do is transfer the license which means legaly no just as the comment said.