Ok, have tested your scene, and unfortunately, here come several problems together:
A. The material, which UE/Datasmith creates for the C4D models is still funky, and needs to be changed, some checkmarks unchecked, others activated (and for convinience, maybe some nodes added to the master material ^.^ )
B. Yeah, you will need to convert your textures to metallic workflow, which… isn´t the easiest way, unless your C4D contains a button, or node or baking function, which let´s you bake out all those textures for metallic workflow. Or… since you already got a texture set, where did you made them? If whatever program you used to create those textures, have the ability to give you the metallic textures, then grab them. I know, that f.e. substance painter can create both specular and metallic workflow sets (Quixel cannot, they use metallic only, maybe switch to them for texture creation;) ).
If neither C4D nor your texture program comes with the luxury of easy conversion, i found an older kind of tutorial, that shows you a more or less accurate way of converting it manually.
Go into the during import created material and
- deactivate “Use_ReflectionColor”, dunno who thought, that this is somehow accurate, but this causes the biggest problems, since until now, the Datasmith plugin cannot recreate any of C4Ds shaders or functions. Maybe it would work, if those shaders etc. could be recreated, but until that happens, turn it off.
- deactivate “Use_Specular”, because C4Ds Specular node has absolutely nothing to do with the specular workflow or specularity, it´s an ancient relic from the Pre-PBR-era to fake specular lights.
- activate “Use_Metallic”, this will give you access to those nodes, where your metal-texture needs to go, or where you define, if your whole material is metal or non-metal, like leather or plastic
- rest of the nodes would be self explanatory, like normal map or ambient occlusion.
Little explanation, what would go where:
- your Albedo/Color/Diffuse texture would go into the Color segment. If you cannot see a texture slot, then activate the “use ColorMap” first, and set mixmode to normal (multiply would mix the chosen color with your texture to give it a different tint). In metallic workflow, the texture would look like a combination of your engine_COL and engine_REFL textures from your model. Any missing texture slot will pop up, if you check “Use xxxMap”
- Reflectance is the segment, thats responsible for the roughness stuff (inverted glossiness), so your roughness texture goes there
- Metallic is the segment, that gets your metal texture (will be a black and white texture, marking segments as either metal or non-metal, usually nothing in between), for this you first have to activate “Use_MetalicMap” (that typo is real ). Or if you don´t have one, use the slider to define, wheter your whole material should be metal or a non-metal.