So you are saying that you start a brand new project file and even there you cannot place a Curtain Wall? That would be very unusual.
If you place the Curtain Wall on top a 2' existing Wall, it should be placed. With Display Order you could decide which one overlaps the other. Also, the Curtain Wall should be visible in 3D.
Can you show some images or put a short video somewhere showing the problem? It might be some small thing we are overlooking. For example, in the Shoe Element in 3D Dialog, Curtain Walls are not enabled to be displayed. Then you go to 3D and place a Curtain Wall and after placement you will not see the result.
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