Learn about using the new GPU Lightmass plugin to bake your lighting. GPU Lightmass improves on the CPU-based Lightmass system by leveraging DirectX 12 and DXR ray tracing capabilities, significantly reducing the time it takes to build complex scenes.
https://dev.epicgames.com/community/learning/talks-and-demos/PG/lighting-with-gpu-lightmass-tips-and-tricks-unreal-engine