Just a quick note, in case it can help anyone else (I spent a day on internet search trying to find this). I was getting stuck with an error that Proton could not run DirectX11, despite installing a reasonable graphics card and up to date drivers. The error message was

"A D3D11-compatible GPU (feature level 11, shader model-5) is required to run the engine"

It turns out that my steam install was running under flatpak, which maintains its own drivers. I needed to do 'sudo flatpak update' and then everything works.

Hopefully someone else can use the info!

System info:
Linux Mint 21.2 (which is an Ubuntu derivative)
Nvidia GeForce2070
Intel i7, 16 GB RAM