https://forum.qt.io/topic/96321/widget-with-qt-popup-flag-ignores-keypressevents-when-mainwindow-is-minimized
Widget with Qt::Popup flag ignores KeyPressEvents when MainWindow is minimized | Qt Forum
Nov 5, 2018 - QtWidgets (5.11) on OS X (Mojave). The combination of setting Qt::Popup WindowFlag to a Widget and minimizing the MainWindow makes the Widget ignore KeyPress...