FNA is using multi-threaded backends by default (I believe in Proton 10.0-3 it uses D3D11, and in experimental, it uses SDL_GPU/Vulkan), and this is working for me without setting the driver.
The main thread isn't stuck in FNA3D code, it seems to end in a WaitHandle:Wait_internal call. So it may be that the program isn't running the main loop while it does some things in the background, but because FNA has to...
I revisited this after learning more about encodings, and it turns out I was completely off base. I found that there's a call to FNA3D_CreateTexture2D that never returns. We are using the OpenGL driver for FNA3D by defau...