Comment by GeekyBear

Proton is just a fork of Wine that also translates from Microsoft's DirectX graphics API to the native graphics API of Linux (Vulcan) so you can run Windows games on Linux.

The new thing Proton is adding is translation from x86 to ARM.

Macs already have Wine, an x86 to ARM translation layer (Rosetta), and an Apple provided translation layer from Microsoft's DirectX to the Mac's native Metal graphics API (D3DMetal) which is integrated into upstream Wine.