Any widget/frame/menu opened from sub-dialog doesn't work on BigSur MacOS. The whole widget is not accessible and clicking everywhere producing a sound like when clicking on blocked parent dialog.

Simple use case:

1) Dialog derived from QDialog
2) open self as a child dialog:

  TestDialog dlg(this);
  dlg.exec();

3) create simple context menu and try to click on any item:

QMenu contextMenu;
	contextMenu.addAction("act1");
	contextMenu.addAction("act2");

	QAction* pSelectedAction = contextMenu.exec(QCursor::pos());
	if (pSelectedAction)
	{
		QString strTxt = pSelectedAction->text();
    QMessageBox::information(this, "clicked", strTxt);
	}

I created a quick test based on TabWidget sample project. Simply click on "btnSubDialog" and then "test" buttons. This will show you the context menu which is not working

When creating a context menu directly from the first dialog, everything works ok.