If you are using NChart3D for iOS, to make the transparency of background work you have to switch off the opacity of the NChartView instance just after you created it:

m_view.isOpaque = false

However this can hit the performance in some cases, because NChart3D is based on OpenGLES and alpha-blending of its grapical content with other UI may be inefficient.

If you are using NChart3D for macOS, you have to set the "Compositing Filter" in the settings of the view in corresponding XIB. The default value of this property is "No Filter", but you have to set for example "Color Blend Mode".