You can make 3D surface maps transparent. The opacity option to control the transparency is available in the colormap settings for the 3D surface layer.

3D surface layers can be transparent using the color properties. In this example, the rectangle is behind the partially transparent surfaces.

To apply opacity to 3D surfaces, follow these steps:

1. Select one of the 3D surface layers.
2. In the Properties window, click on the General tab.
3. In the Material Color section, click the Custom Colormap button (...) to the right of Upper.
4. Change the Opacity value to adjust the opacity of the entire colormap.
   
   Alternatively, double click in the opacity map to add more nodes, then change the Opacity value for each node individually.
   
5. Click OK, and the opacity is applied to the layer.

Updated December, 2021