On OS X 10.15.7 running Mathematica 12.1.1 when I set $UnityExecutable = "/Applications/Unity\\ \ Hub.app/Contents/MacOS/Unity\\ Hub" I get the error message UnityLink; Unable to find the Unity game engine for LaunchUnity["ExampleData/roll-a-ball"] or LaunchUnity[].
So does Mathematica 12.1.1 not work with UnityHub - as opposed to Unity?