You can play 64-bit macOS Steam games using ... Steam for macOS. This works fine (at least until they kill Rosetta2), though you are still translating x86.
And most Windows Steam games (32- or 64-bit) via Crossover. (Expect about half the frame rate of a native ARM/Metal port at the same settings.)
But you may be asking whether you can run Proton well in a Linux VM. I think it would depend on having a good Vulkan implementation that works well with a hardware GPU, so I expect the answer is yes with an eGPU, no with the internal GPU.
> You can play 64-bit macOS Steam games using ... Steam for macOS
Assuming they are kept updated. Unfortunately, the way macOS works is that Apple expects developers to constantly update their apps to keep them working on newer macOS versions, and for games especially this is often not the case a few years after the release.
Worse yet, many titles are marked as working, but if you actually try to use them, various things break, e.g. hi-DPI.
And most Windows Steam games (32- or 64-bit) via Crossover. (Expect about half the frame rate of a native ARM/Metal port at the same settings.)
But you may be asking whether you can run Proton well in a Linux VM. I think it would depend on having a good Vulkan implementation that works well with a hardware GPU, so I expect the answer is yes with an eGPU, no with the internal GPU.