How to draw opaque background with WA_TranslucentBackground active

[Maryu]

Edit: forgot to add - I am using Qt 5.15 under Windows 10 MSYS2 MinGW

I have a QMainWindow subclass with

setAttribute(Qt::WA_TranslucentBackground);

setAttribute(Qt::WA_TranslucentBackground);

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in its constructor. I want the widgets to be transparent by default, which works. But now I want to add a special widget, say the member "QWidget* m_opaque;", with a fixed non-transparent background color. However even with

• m_opaque->setAutofillBackground(true);
• m_opaque->setAttribute(Qt::WA_OpaquePaintEvent);
• m_opaque->setWindowOpacity(1.0);
• m_opaque->setStyleSheet("{ background-color: grey; }");

the widget still has transparent background .. how do I make it opaque?