u/Arthandas

Put this in Engine.ini:

[ConsoleVariables]
r.ContactShadows.NonShadowCastingIntensity=1 ; basically more contact shadows, default is 0
r.MotionBlurSeparable=1 ; adds a 2nd pass that smooths noise for a higher quality blur, default is 0
r.Tonemapper.Quality=1
; 0: basic tonemapper only, lowest quality
; 1: + FilmContrast
; 2: + Vignette
; 3: + FilmShadowTintAmount
; 4: + Grain
; 5: + GrainJitter = full quality
; To disable vignette it can't be set higher than 1, default is 5.
r.ViewDistanceScale=2 ; reduces pop-in, default is 1

This goes into GameUserSettings.ini:

[VolumetricFog@HIGH]
r.VolumetricFog.GridPixelSize=6
; Decreasing it improves general quality of volumetric fog (which is used basically everywhere),
; especially noticeable on volumetric light shafts. Going below 6 starts to have a noticeable
; performance impact and is not worth it as light shafts are generally pretty rare. Default is 8 (on
; the highest in-game settings).

Album with comparison pics:imgur .com/a/stellar-blade-tweaks-unqknMU

(the screens are darker than normal since I play with HDR on and had to save them in a non HDR format - if you use HDR don't forget about RenoDX)

Contact shadow pics were taken from this post

Probably the most impactful tweak is removing this overbearing vignette. Overall performance impact is minimal.