I did some extensive testing and think that "texture streaming" seems very responsible.
with the following settings i've stable 90fps with no jittering at all. head movement is smooth.
<antialiasing taa="true" checkerboard="false" cmaa2="false" dlss="false" cas="0" fsr="1" fsr2="0" />
<dlss_quality value="2" />
<dlss_sharpness value="0.800000" />
<fsr_quality value="1" />
<fsr_sharpness value="0.250000" />
<dynamicresolution_enabled value="false" />
<dynamicresolution_target_fps value="0" />
<dynamicresolution_profile deltaDown="0.05" percentageDown="0.85" deltaUp="0.01" percentageUp="0.8" alpha="0.95" />
<dynamicresolution_min_scale value="0.5" />
<ssao enabled="true" algorithm="2" />
<ssrt enabled="true" quality="3" />
<texture_streaming sizeInMiB="1024" texelDensityBias="0.0" concurrentTextureSwaps="1" />
<led_display fanatecNativeSupport="true" sliProNativeSupport="false" sliProForceBrightness="127" />
<anisotropic_filter level="16" />
<lighting quality="2" volumetricFogLighting="true" volumetricFogLightMapWidth="512" volumetricFogLightMapHeight="256" volumetricFogLightMapDepth="32" />
<postprocess motionBlur="false" godRays="true" depthOfField="true" lensStreak="false" lensFlare="true" bloom="true" />
<shadows enabled="true" skyShadowMapSize="2048" skyShadowCascadeCount="4" skyShadowLowLod="false" worldShadowMapSize="2048" skyShadowMap32Bits="true" nightShadowMapSize="2048" nightShadowCharacterCast="true" nightShadowSourceCount="4" sampling="1" spotShadowMapSize="1024" spotShadowSampling="1" crowdInShadows="false" />
<particles enabled="true" distanceScale="1.0" rate="1.0" high="true" />
<crowd distanceScale="1.0" billboardDistance="1500" />
<vehicle_reflections envMapScale="1.0" envMapUpdateMode="alternate" envMapRenderMode="carsAndCharacters" cubeMapEnabled="true" cubeMapScale="0.75" cubeMapUpdateMode="oneAxisPerFrame" />
<mirrors mirrorsUpdateMode="alternate" mirrorsRenderMode="carsAndCharacters" treesInMirrors="true" crowdInMirrors="true" highDetailMirrors="false" highDetailTyresAndCar="true" particlesInMirrors="false" />
<weather_effects rainSplashes="true" rainSheets="true" rainBeads="true" rainHigh="true" trackHeatHaze="true" planarReflectionsEnabled="true" planarReflectionsHQEnabled="true" planarReflectionsRangeScale="1.5" planarReflectionsRTScale="0.5" planarReflectionsMipTailBlur="true" proceduralCloudRTScale="2.0" proceduralCloudTiling="7" proceduralCloudQuality="1" />
<ground_cover enabled="true" grassFlattening="true" drawDistance="120.0" meshes="true" />
<skidmarks enabled="true" parallax="true" />
<skidmarks_blending enabled="true" />
<audio audioUpdateRate="2" numHelperThreads="8" />
<async_compute enabled="true" />
<cs_culling enabled="false" />
<vendor_shader_pack enabled="true" />
<replay_directory path="" />
<rt_quality quality="3" />
<rt_shadows enabled="false" />
<rt_reflections enabled="false" />
<rt_transparent_reflections enabled="false" />
<rt_ao enabled="false" />
<rt_version version="0" />
Win11, RTX3090, Reverb G2