hi @Shinjuku007 ,
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You need the Lighting important volume to select an area for GPULightmass to render.
Currently to are attempting to render the whole Scene . Using Several LIV each will be processed
WTF Is? Volume - Lightmass Importance in Unreal Engine 4 (youtube.com)
Read the original
Gpu Lightmass Global Illumination In Unreal Engine | Unreal Engine 5.4 Documentation | Epic Developer Community (epicgames.com)
Read the new
Download the ‘Lighting in Unreal Engine 5 for Educators and Students’ guide
The Epic GPULightmass forum
Epic’s GPUlightmass - Development / Rendering - Epic Developer Community Forums (unrealengine.com)