No worries! But I think I might have misread your post? If you're on MacOS 11 or above, you should be able to run the game fine.
So, in Gamemaker (our engine), there's a certain method of compiling that's required to make a Steam build. (Specifically: VM vs YYC. VM being the build on here, YYC being the build required for Steam)
Trying to test that build on our 10.15 Mac tells us that 11.0 or later is required to run the application.
We haven't tested it on Steam yet, but we assume it'll be the same as trying to run it from the desktop. Maybe it might be something to do with our settings. We'll be sure to look into it more!