Just tested 5.4 (main) and the IES lights are still broken so for Archviz 5.1 is the only option at the moment if you prefer GPUlm instead of Lumen (for instance to build for mobile VR or high-framerate desktop VR).
Reported a while back but in the Unreal Bug Tracker its still noted as fixed (for 5.1 - it was broken as well in 5.0).
Can I ask if anyone at Epic is aware of this issue? Also, is GPUlightmass still under development? Not much going on in this forum. Also, I can’t remember if there were any updates in 5.2 and 5.3 for GPUlm besides the AO-like-issue that was fixed…