The background cannot be transparent

I am doing mixed development of MFC and Qt components. I ran the following example https://github.com/qtproject/qt-solutions/tree/master/qtwinmigrate/examples/winwidget
When testing the Qt component embedded in the Windows standard window, the background cannot be transparent. If the QWinWidget is set to transparent, the display on the form will turn black. This is normal in a pure Qt program, but there will be problems when mixed with Windows standard components or MFC. Can this problem be solved? I want to make the QWinWidget background transparent