My understanding about the game porting toolkit is that it requires developers to specifically modify their game in order to make their game compatible.
The magic of Proton from a consumer point of view is that it just works for basically every game, sans those with Kernel-level anticheat stuff. This means thousands of old games that haven't been updated in years will work.any games that don't have active developers.
So Apples solution works for new games but isn't a practical option for compatibility for existing games.
There is things like whisky app which makes it a more general thing like proton
crossover experience does not require manual modification by developer
The stated intended purpose of the game porting toolkit is to enable developers to modify their games. But the software actually being shipped includes what is literally a Wine GPU backend, which is usable by (and already used and bundled by) consumer-facing Wine applications like Crossover. If you go to Codeweavers, download any Crossover for Mac from the past year (Sep. 27, 2023 according to their release notes), you're getting a tool that includes the D3D to Metal layer from Apple's Game Porting Toolkit.