Photogrammetry LOD, which is tied to terrain LOD, hammers the main thread. That’s why I created a suggestion for the developers to untie them, but it may not be possible or likely:
https://forums.flightsimulator.com/t/suggestion-for-performance-optimization-make-terrain-lod-only-affect-terrain-and-ground-textures-with-separate-lod-sliders-for-other-things/509780
When on the ground, dynamic LOD may be the best and easiest solution.