Hi @MeanLemur
You need to complete the setup in
GPU Lightmass Global Illumination in Unreal Engine | Unreal Engine 5.3 Documentation
This is Same for
Luoshuang’s GPULightmass - Development / Rendering - Epic Developer Community Forums (unrealengine.com)
LGPU Lightmass
and the Epic GPU Lightmass
The LGPU is based on Nvidia card other cards need to use CPU Lightmass or Epic GPU Lightmass