I've never really thought about whether the game looks the same using its Windows vs Linux renderer. I installed HL2 to check out the anniversary update and decided to try the Windows renderer on Proton. Would you look at this difference... Linux is the top one, Windows is the bottom:
Is this is a thing? Have you tried other games and seen the Windows version looking better?
Thevideo settings are the same on all configurable options. They're set to max.
I think this is likely the reason. Which makes me think this sort of difference might exist across other games that use D3D on Windows and GL on Linux. Difference in Capabilities along with time spent making something look the way the developers want it to look on those capabilities. So if they spend a lot more time on the Windows version, they might fix things to look alright on D3D and leave them be however they turn out on GL.