If I use a QAxWidget inside of a window with attribute Qt::WA_TranslucentBackground the whole ActiveX element is transparent. Normally it should have a white background.
This is what we get if we use a QAxWidget by it's id without translucent background. The white widget is a control from a signature pad.
This is what we got with translucent background: The signature widget is completely transparent. (But it works nevertheless)
Note about the example: I've included the ocx file from https://www.signotec.com/ api which needed to be registered in windows before.