the eye is on an untextured background (I forgot the specific therminology)
but yet it is displayed ad being black
on the node editor, the background, is something else, not black
but yet on the 3d viewer it is displayed as being black
Have you tried plugging in the Alpha Socket from the texture… Into Alpha on the Principled Node.
See how the top two images are black all around the eyes - but the photoshop image shows transparency… Plug in the Alpha.