Noob question : why are my Cycles render too bright, even with no lights? Why are my Cycles render so bright, I even tried to erase all lights and it makes no difference... :(

Below render example. It's supposed to be a commercial kitchen. Looks great with Eevee but with Cycles looks like big snow storm...
It looks like you have inadvertently enabled the Ambient Occlusion setting in the World properties. Disable Ambient Occlusion again and all should be fine.