Better and optimized Graphics Version:

So since after 3 years nothing has happened in the direction of fixing graphic errors, I have now taken a somewhat harder path here in the ini: First of all: All graphic errors are gone now, really all of them. The blue flashing and shimmering trees behind dark clouds were particularly disturbing. Which caused trees to shimmer blue when it rained or snowed. Even in sunshine flickered, pixel errors appeared on the horizon. Power lines also flickered. Now I have disabled the volumetric clouds and all these errors are gone in one fell swoop. It's raining and snowing now with a cloudless sky. The second was the acne shadows, the contact shadows are to blame here. I disabled the contact shadows and enabled all distant shadows. They're completely gone now too. To 100%. And I also fixed the bug with the liquid shadows. The problem with scum is that it has a lot of errors, technically. Also the lod, lighting, wpo, bias, and many, many other things. I was able to eliminate them so far that it now plays comfortably. I've increased the cull and grass distance extremely, don't worry, it doesn't cost any performance. On the contrary. Since I optimized the lighting, I was able to get 20 fps there alone. In addition, removed lod that is not visible is no longer calculated, which again resulted in about +15 fps. This gave me leeway for the lod and the grass. My options via the ini are limited, so this is all that is possible. If you want the clouds and the graphic errors back, you can simply reactivate both volumtric clouds settings. For my part, I'm done here for now.
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Add this to User/Name/AppData/Local/Scum/Saved/Config/WindowsNoEditor/Engine (leave one line blank):

[SystemSettings]
r.Streaming.Boost=1
r.FastVRam.EyeAdaptation=1
r.bForceCPUAccessToGPUSkinVerts=1
r.Streaming.HLODStrategy=0
r.Streaming.LimitPoolSizeToVRAM=1
r.Streaming.MaxEffectiveScreenSize=0
r.Streaming.UseFixedPoolSize=1
r.Streaming.PoolSize=6144
r.Streaming.MipBias=0
r.Streaming.DefragDynamicBounds=1
r.HZBOcclusion=1
r.MaterialQualityLevel=1
r.EmitterSpawnRateScale=2.0
r.DetailMode=2
r.MipMapLODBias=0
r.HLOD=1
r.HLOD.DistanceScale=1.5
r.HLOD.MaximumLevel=1
r.MaxAnisotropy=16
r.ViewDistance=2
r.ViewDistanceScale=2.0
r.LandscapeLODDistributionScale=2
r.LandscapeLOD0DistributionScale=2
foliage.LODDistanceScale=1.85
foliage.ditheredLOD=1
grass.CullDistanceScale=1.75
foliage.MaxOcclusionQueriesPerComponent=128
foliage.MinInstancesPerOcclusionQuery=65536
foliage.MinimumScreenSize=0.00000001
r.StaticMeshLODDistanceScale=0.50
r.SkeletalMeshLODBias=-2
grass.DisableDynamicShadows=1
grass.DensityScale=0.75
foliage.DensityScale=1.0
r.Water.WaterMesh.TessFactorBias=12
r.HairStrands.DeepShadow.SuperSampling=1
r.Fog=1
r.FogDensity=0.02
r.FogStartDistance=4
r.VolumetricFog.GridDivisor=30
r.VolumetricFog.GridPixelSize=8
r.VolumetricFog.GridSizeZ=64
r.VolumetricFog.Jitter=1
r.VolumetricFog.InjectShadowedLightsSeparately=1
r.VolumetricFog.InverseSquaredLightDistanceBiasScale=1.000000
r.VolumetricFog.LightFunctionSupersampleScale=2.000000
r.TrueSkyQuality=1
r.SkyLightingQuality=1
r.SkylightIntensityMultiplier=0.4
r.VolumetricCloud=0
r.VolumetricCloud.SkyAO=0
r.ShadowQuality=4
r.Shadow.CSMDepthBias=20
r.Shadow.FilterMethod=0
r.Shadow.DistanceScale=3.0
r.Shadow.RadiusThreshold=0.01
r.Shadow.MinResolution=2048
r.Shadow.MaxResolution=2048
r.Shadow.FadeResolution=2048
r.Shadow.PreShadowResolutionFactor=1.0
r.Shadow.AllowForegroundShadows=1
r.CapsuleShadows=1
r.CapsuleMaxDirectOcclusionDistance=600.000000
r.CapsuleMaxIndirectOcclusionDistance=400.000000
r.CapsuleShadowsFullResolution=1
r.Shadow.PerObject=1
r.DistanceFieldShadowing=1
r.DFShadowQuality=4
r.DFFullResolution=1
r.ContactShadows=0
r.DistanceFieldAO=1
r.AllowLandscapeShadows=1
r.AmbientOcclusionLevels=2
r.DefaultFeature.AntiAliasing=2
r.PostProcessAAQuality=6
r.ScreenPercentage=100
r.TemporalAASamples=32
r.TemporalAACurrentFrameWeight=0.12
r.TemporalAAFilterSize=1.0
r.TemporalAACatmullRom=1
r.TemporalAAPauseCorrect=1
r.NGX.DLSS.Sharpness=0.25
r.NGX.DLSS.EnableAutoExposure=1
r.BloomQuality=4
r.ParticleLightQuality=2
r.RefractionQuality=2
r.LensFlareQuality=3
r.LightShafts=1
r.LightShaftQuality=2
r.LightMaxDrawDistanceScale=3
r.TransluzenzLightingVolumeDim=4
r.EyeAdaptationQuality=2
r.SSR.Quality=3
r.SSR.MaxRoughness=1
r.SSS.Scale=1
r.SSS.SampleSet=2
r.SSGI.Quality=3
r.Color.Mid=0.35
r.SceneColorFormat=4
r.TonemapperGamma=2.2
r.Tonemapper.Quality=3
r.TonemapperFilm=1
r.FastBlurThreshold=0
r.MotionBlurQuality=0
r.MotionBlur.Amount=0
r.MotionBlurSeparable=0
r.DepthOfFieldQuality=0
r.DepthOfField.FarBlur=0
r.DefaultFeature.MotionBlur=0
r.SceneColorFringe.Max=0
r.SceneColorFringeQuality=0
r.MotionBlur.Max=0
r.Tonemapper.GrainQuantization=0

[/script/engine.userinterfacesettings]
ApplicationScale=0.75
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If you want the clouds, pixel errors and foliage blinking back, just change the following:

r.VolumetricCloud=1
r.VolumetricCloud.SkyAO=1

And if you want to have the distance acne shadows (=technical term) back with liquid indoor shadows:

r.ContactShadows=1

If you have activated the contact shadows again, you have to deactivate the distance occulision again ingame, otherwise you will have the liquid shadows again. Without contact shadows they work correctly.
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Nvidia:
Activate dlss quality and not dlss ultra quality. Ultra quality Mode have low resolution.

AMD:
AMD FSR Quality works well.
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Color and brightness optimization of the system:

Ingame I selected the gamma value 2.20, which is the standard. 2.40 is too high.

Nvidia: Go to digital color enhancement (desktop color setting) and select a value between 60-80%.

Go to Change Resolution, scroll down and select: Nvidia Color Setting. Dynamic Output Range: Full. Color format: RGB.
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Have fun with the better Graphics.