I download the arfoundation-samples-master sample package and try the sample scene HumanSegmentationImages.I left all inspector setting as default, Build by Unity 2019.2.8f1,Xcode 11. It only shows a white image in front of a normal camera view. In TestDepthImage.cs, I add debug script to get m_HumanBodyManager.humanStencilTexture and m_HumanBodyManager.humanDepthTexture, it shows null.
Problem solved after I change ARFoundation 3.0.0 preview 3 to preview 4.