I am doing tests of the gpulightmass that I create unreal engine in 4.26p1, it is necessary to have an nvidia card that supports RTX at the moment. being able to adjust the lights and see the preview in real time is one of the best aids for architectural visualizations. still has some bugs but it will be important for the workflow in the future.
Unreal Engine 4.26 Preview - Unreal Engine Forums To enable GPU Lightmass: Enable Ray Tracing and set the Default RHI to DX12 in the Project Settings. (Requires a DXR capable graphics card with Windows 10 build 1809 or later.) Enable Virtual Texture Lightmaps project setting for real-time preview in the editor. Enable the GPU Lightmass plugin. Recommended to set r.RayTracing.ForceAllRayTracingEffects 0 in the editor to disable all ray tracing effects. This helps give more resources to GPULightmass and avoids some confusion between features, such as ray tracing soft shadows rendering on top of lightmaps.