Hi,
I am also using QT (pyside2) to development a tool for Blender. The purpose is also to have it able to be stand-alone.
I am also facing the same problem in blender. The QT window cannot be parent / on top of the Blender. I tried the QT.WindowsStaysOnTopHint flag, it is not what I want as it freeze the blender out of the QT window.
Is there any solution you found and can share?
Thanks.