The way games on Linux work today is most are compiled for Windows. There are a few exceptions like Civ will in many cases provide a fully Linux native build. But even in that case on Linux you can choose whether to run the native or the Windows version.

When you download a Windows game on Steam you will go into the Settings and select "Compatibility Layer" and there you will find several versions of Proton. Proton https://github.com/ValveSoftware/Proton is a pre-configured wine bundled with windows DLLs and Linux .so library files. This makes Proton Immutable for any given major version. Meaning you can run Proton 2.x for your game if that's what fits your situation. It's always there if you need it for your specific games. Steam launches this in a container. It is not emulated. It is a fully native implementation of the API that in many cases achieves superior performance.

This is why you will sometimes see the joke that the most compatible API for Linux is actually the w32 API.

This API is now at the point where pretty much everything works unless you cripple it on purpose. And that's what Epic Games is doing here. There's no technical reason for this. It's a business decision that doesn't even make sense because frankly I could vibe code them a linux native game client that launches their games properly on linux in a few days.