Deactivate QMenu self-selection

That effect is thrown by the event QEvent::MouseMove in the QMenuBar, if you want to discard it you have 2 possible solutions: the first is to create a class that inherits QMenuBar and overwrite the mouseMoveEvent() method eliminating that task, and promote it so that it use Qt Designer, another simpler solution is to use an event filter, and that's what I'm going to show.

Assuming the code of your previous question that I answered Then the solution is the following:

class Principal(QMainWindow):
    def __init__(self):
        QMainWindow.__init__(self)
        uic.loadUi("nuev.ui",self)

        self.menuBar().installEventFilter(self)

    def eventFilter(self, obj, event):
        if obj is self.menuBar() and event.type() == QEvent.MouseMove:
            return True
        return QMainWindow.eventFilter(self, obj, event)


if __name__ == '__main__':
    import sys

    app = QApplication(sys.argv)
    p = Principal()
    p.show()
    sys.exit(app.exec_())

We return True since we want that event not to be handled by the QMenuBar, if we restart False we tell it to handle it.