Apple wouldn't do that though because that means no platform lock in. Even though something like Proton for Mac would be a gamechanger for many of Apple's customers, Apple care more about ensuring developers lock IN to the Apple specific technology ecosystem by building Metal specific Apple-only games rather than expanding Mac's reach OUT into the already existing AAA game market.
This doesn't make sense. If I really want to lock in people in my new platform, then a very effective strategy is to make customers need the other platform less and less while using my platform for everything. The way it is, Apple is forcing you to pick a Windows machine if you want high-performance gaming. It would be ideal for them if their platform could do everything a Windows PC can do, while still having features only they offer. Why would I buy a Windows PC and an Apple PC / device if I can just keep an Apple-centric workflow?
Microsoft gets most of this right. For example, they are actively developing a good WSL (Windows subsystem for Linux). This means that not only you can run Linux within Windows, but do it with very good performance, killing any need for dual boot. And soon, you'll be able to even run Android apps there. And to top it off, they are developing WSLG, which allows you to run graphical Linux programs with hardware acceleration and no extra configuration (right now, getting graphical applications to run under WSL is annoying).
It baffles me that Apple is not integrating virtualization to offer a permanent solution for gaming without much extra effort. They have so many cores at this point, and virtualization has so much to offer – even from a security standpoint.