Rendering in Nvidia or Texture shade
When you do a render, do you render in Nvidia or texture shading? I will be building a Ryzen 3950x with a MSI X570 unify motherboard... RTX 2080ti... 96gb of ram... 3 Samsung evo 970 plus M.2... with a Noctua NH D-15 dual Chromax black fans....

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What do you mean? Texture Sahded is a preview mode, Iray can be used for a preview but is usually thought of as a render option. Are you thinking of 3Delight, or even the OpenGL modes?
I was wondering because of some models when in Nvidia mode, they would stay white and don't show the textures, but in shader mode they all reappear.
That would, I think, be down to the shader used - if they use a custom 3Delight shader then DS would not be able to translate it into an Iray equivalent. If this is only in the Iray Preview mode, and they render correctly, it may be down to Draw Settings (which controls the preview).