The Game Porting Toolkit is weird because despite first appearances it doesn't actually help developers make quick ports. Apple built a pretty robust DirectX-to-Metal shim, but they only licensed it for "evaluation purposes", so its only value to developers is in seeing whether their Windows game runs well enough on Macs to be worth porting. If they do decide to port they still have to do it the hard way, they're not allowed to ship Apples shim to users.

It's kind of baffling because it does almost nothing to help the game developers that it's ostensibly aimed at, while it does help end-users play unmodified Windows games on their Mac, which Apple doesn't endorse.