For my setup I’ve read and implement the tips from UE Docs :
https://docs.unrealengine.com/4.27/en-US/Resources/Showcases/ArchVisInterior/
https://docs.unrealengine.com/5.0/en-US/hardware-ray-tracing-tips-and-tricks-in-unreal-engine/
I’ve already test some settings, one by one, but I didn’t find what goes wrong now, but I know RTGI sample affect the patterns (white spots). I see if it’s a question of material setting (normal) …