So basically I've got a separate Steam installation on another folder on my Desktop, that's the one I launch with Sandboxie.
I made a shortcut to that, and ensured it runs as administrator and placed "-initbootstrap" in the target.
I then ran the shortcut:
And then after I logged into Steam (second account), I ran the second version of the game like so:
I'm also clicking "Run as UAC Administrator" for everything I'm running in Sandboxie.
Unfortunately even after all that, it's still not working. Second game client does not want to connect to Steam.
Are we sure at this point that it's not the runner/GameMaker doing something that's not allowing it to connect to Steam? Maybe it has something to do with the Steam App ID? I couldn't find out where to type it in in GMS2:
Are my game options fine?
Also my Steam SDK version:
And my GMS2 IDE/Runtime versions: