In post 10 of the initial post Lumen GI and Reflections feedback thread - Development Discussion / Unreal Engine 5 Early Access - Unreal Engine Forums the instruction was given
Lumen’s use of ray-traced direct lighting is tied to the use of ray-traced shadows in the scene. You can decouple this by setting the following CVar:
r.Lumen.DirectLighting.HardwareRayTracing 0However, you might opt to work without ray-traced shadows, since virtual shadow maps are the preferred method to use with Nanite assets.