[QUESTION] What is the most realistic-looking game that can also run on Linux distros?

Cyberpunk 2077, probably. The game maxed out will destroy your graphics card but the graphics are undoubtedly gorgeous.
Horizon Forbidden West also has really good graphics.
- I second Horizon. There are moments where I’m convinced the graphics are pre-rendered when cranked to the max.
- I second Cyberpunk, ray tracing enabled or not. That game truly captures a realistic dystopian world in the best way possible.
- I just started playing ghost of tsushima on my steam deck and it's fucking gorgeous even on low settings, so I assume that would be pretty beautiful maxed out too.

Alan Wake 2 is probably the best looking game running on any system, it works on Linux via Proton

You can look for specific games on protondb.com to get a good idea of how they run.
I don't chase high-end PC gaming anywhere near enough to name a single game that is known for realism.

I know it's a meme but I just checked and crysis remastered is supposed to run on linux.

The facial animation in Hellblade: Senua's Sacrifice is still the best I've ever seen, and that game came out in 2017.
Incredible looking game. I hope the sequel lives up to the original.
- It was barely a game though.

I'll answer your question with another question: What is the most realistic-looking game?

I'm not on linux, but I heard star citizen works and it's running a free to play event right now until the 26th of May.
If you don't like Easy Anti Cheat I would avoid it.
- I don't have a problem with anti cheats. I just hate the ones blocking Linux on purpose.