I have absolutely NO idea who makes or distributes these material room setups, but EVEYTHING between the Diffuse texture and the Posersurface has to go.

In the render settings? Is there a mirror somewhere? Glass? No? Then Raytrace bounces can stay at 1. Uncheck Irradiance Caching. Min Shading Rate => Set to 1 for draft, and 0/5 for medium, and 0.2 for extra sharp renders. Bucket size at 32 is the best default. (You can use 64, 128 for single naked figures) But lower bucket size when the scene fills up. Post filter size set at 3 and Filter Type at Sync. Always render with IDL to ON and GC at 2.2. That part is good.

But for IDL to work properly, you have to have a filled scene. The extra diffuse light has to come from somewhere. When you have an empty scene, with only a naked figure, there is no "extra" diffuse light for IDL to work as it should.

Actually, a figure skin is SUPER simple to set up and requires only a few basic nodes. (all what you see in the Mat room screengrab above is faking, and all that faking has to go out when you render with IDL.)

The rest of the light has to come from the rest of the scene. (as it does in the real world) => That is DIFFUSED light. => That is what we see in the real world.

The last render does not look like skin. It looks like wax.