Longer answer: There has already been a decent effort trying to reverse engineer the relevant parts of the game engine and port them to more modern engines. Check out
github.com/MBU-Team/OpenMBU/
for the MBU team's work reversing Marble Blast Ultra (with some MBG compatibility). Various people have ported the engine's systems to other languages, such as the nearly-complete rewrite in Haxe by RandomityGuy:
github.com/RandomityGuy/MBHaxe
and the more clean-room rewrite by Vanilagy (with different physics) at
github.com/Vanilagy/MarbleBlast
Other than that, if you want to try contributing to the reversing effort, there are various copies of MB floating around in much easier to port forms than just the MBG exe. You might be able to find one if you DM the right person, but it's unlikely they would be posted in public, considering copyright etc.
If all you want is to play MBG on modern versions of macOS, I would recommend using the Windows version of the game and some form of Wine (eg Crossover). It's relatively performant for the base game considering it was written for 2003 hardware. It even works on the M1 via Rosetta translation.