Alt modifier doesn't work in shortcuts on MacOS with parent-less menubar

I am experiencing the same issue that has been reported here: https://bugreports.qt.io/browse/QTBUG-45453.

I am programmatically creating an "Alt+X" shortcut using the setShortcut method, but it is not being triggered.

This problem occurs when using a menubar without a parent, however it does not happen with the menubar provided by the QMainWindow class.

Since our application does not have a main window, one workaround is to set an eventFilter on the application, which is not fully satisfactory (also, the menu does not flash).

I have attached a similar example to the one in the link above.

I am using macOS 10.15. I have checked that this issue occurs with all of: Qt 5.9.9, Qt 5.15.2, Qt 5.15.10, and Qt 6.2.4.