That's not a bug, at least not from a technical point of view, I find this a really huge sale bug: by default, those fads have material that is thought only for Firefly, as they have Amient _occlusion nodes, which are not supported by the RTX mode. I have an old RTX2080Ti and the effect is the same.

Most of the time I rebuilt the textures, especially for the skin and for the cloths.  Ghostship is selling fantastic Cycles-based materials, and they are a good start.

Another good start is to look at Rendo's tutorials: you have really simple material setups, involving the Physicalsurface node, for which you only need a diffuse map and a bump map for a good start.

As a proof: I've only deleted those nodes, and unchecked both options (red arrow, I'm using my scripts for these two operations)

You end up with a decent, RTX-mode enabled render: