Why does the lighting do not work? it worked before but I decided to turn up samples and turn on denoising and such because it had to much noise/ white pixels and then after that the render is so dark. Here is the blender file
I am not sure, but i think you clamped the light too much.
I got this:

if i increase your clamping (clamping direct and indirect light) from 0.03 to 0.2