LMU Graphics Best Settings

Video Device: 6900XT - you also want to underwolt this one or possible other AMDs. Use LACT for this.
My case: 7680x1440@120hz on X11 (6900XT with Ryzen 9800X3D) (GPU offset -81 via LACT app)
Steam launch: mangohud gamemoderun %command%
(LACT does the underwolt if you set, gamemorun has other benefits, like blocking screen saver)

You want a 9800X3D for LMU, it is a beast, I upgraded from a 5800X3D - It's like 50% better, LMU is Single-Core CPU bound 
most the time, very noticeable on night races, eg. Paul Ricard last corner at dark.

Before opening the game (if game is running changes get overwriten), edit: 
~/.local/share/Steam/steamapps/common/Le Mans Ultimate/UserData/player/Settings.JSON
"Headlights On Cars": false, #Just in case, dunno if's an active change.
"Max Headlights": 2, (Only my car has front healights, massive gains and looks better. If you use mirrors 2 may be not enough.
"Max Framerate": 120.0, (In my case)

Start game, and game settings:
Vertical Sync: Off
Fullscreen (Important on KDE on single monitor, otherwise kwin keeps interfering, windowed for triples.)
#I found out LXDE worked best for gaming due to non intrusive WM, but it is a good amount of work to set it up properly.
Post processing: Low
FSAA: MSAA 4x
FXAA: OFF
MultiView: OFF (ON for Triples)
Display VR Mirror: OFF

(Ultra VRAM 16G is not enough on big circuits)
Circuit Detail: High
Texture Detail: High
Player Detail: High
Opponent Detail: High 

Texture Filter: 8x
Texture Streaming: On

Special Effects: Mid
Shadows: OFF #IMO shadows in LMU look horrendous anyway.
Shadow Blur: OFF
Soft Particles: OFF #Gimmicks, just makes game generated smoke more 'smokie'
Rain Drops: Medium
Road Reflection: Low
Environment Reflection: Low

Visible Cars: 17 if 9800X3D, other cpus better 12.

#Bellow is a full cache cleaner, you may run it after doing bigger graphical changes:
slemke@gamingpc:~> cat clear-cache.sh 
#!/bin/bash 

#Clear Steam's global shader cache
rm -rf ~/.local/share/Steam/shadercache/*

# Clear a specific game's shader cache (replace <AppID>)
rm -rf ~/.local/share/Steam/steamapps/shadercache/*

# Clear DXVK cache for a Proton game
rm -rf ~/.local/share/Steam/steamapps/compatdata/2399420/pfx/drive_c/users/steamuser/AppData/Local/dxvk

# Clear Mesa OpenGL cache
rm -rf ~/.cache/mesa_shader_cache/
rm -rf ~/.cache/radv_builtin_shaders

rm -rf ~/.steam/steam/steamapps/common/"Le Mans Ultimate"/UserData/Log/Shaders
rm -rf ~/.steam/steam/steamapps/common/"Le Mans Ultimate"/UserData/Log/trace*

#Remove practice sessions from replays
rm -rf ~/.steam/steam/steamapps/common/"Le Mans Ultimate"/UserData/Replays/*P1*