You can run external games using Steam's Proton[1]. It's not mentioned in the article so I guess it's not any help?
[1] https://boilingsteam.com/valve-breaks-the-shackles-of-proton... or you could in 2019, anyway
Proton is implemented via Wine - it's like a collection of software and automatic configuration. You use Wine to implement Windows syscalls. Wine also has DXVK to convert the DirectX calls to Vulkan ones. So it's all the same stuff really.
https://github.com/ValveSoftware/Proton/
wine @ eef39a6 vkd3d-proton @ 72d9b32
Cobbling together existing tools is really powerful in games and graphics :)