If you turn on “Double-sided” with a material whose surface is inverted and invisible, it will turn black.
(The door part is mainly inverted.)
If you look at a similar post, I think it’s because you can see the back side that is not exposed to light.
At present, I think it is necessary to correct it with CAD software,
It would be great if we could add features that could be fixed in Shapespark.
The CAD software maker has asked me to modify the FBX file in the destination application.
We would appreciate it if you could consider it.