For demo purposes, with pointer handling turned off:
====================================================

"5.12.0 windows" ("-platform", "windows:nowmpointer")
Qt::StrongFocus
QWidgetWindow(0x2a6c89b5400, name = "QMainWindowClassWindow") QFocusEvent(FocusIn, OtherFocusReason)
QWindowContainer(0x2a6c64a1000) QFocusEvent(FocusIn, ActiveWindowFocusReason)
QWindowsVistaStyle(0x2a6c649d510, name = "windowsvista") QFocusEvent(FocusIn, ActiveWindowFocusReason)
QWidgetWindow(0x2a6c89b5400, name = "QMainWindowClassWindow") QFocusEvent(FocusAboutToChange, OtherFocusReason)
QWindowContainer(0x2a6c64a1000) QFocusEvent(FocusAboutToChange, OtherFocusReason)
QWidgetWindow(0x2a6c89b5400, name = "QMainWindowClassWindow") QFocusEvent(FocusOut, OtherFocusReason)
OpenGLWindow(0x2a6c649f610) QFocusEvent(FocusIn, OtherFocusReason)
QWindowContainer(0x2a6c64a1000) QFocusEvent(FocusAboutToChange, OtherFocusReason)
QWindowContainer(0x2a6c64a1000) QFocusEvent(FocusOut, OtherFocusReason)
QWindowsVistaStyle(0x2a6c649d510, name = "windowsvista") QFocusEvent(FocusOut, OtherFocusReason)
OpenGLWindow(0x2a6c649f610) QEnterEvent(QPoint(18,33))
QWidgetWindow(0x2a6c89b5400, name = "QMainWindowClassWindow") QEnterEvent(QPoint(29,23))
QMainWindow(0xc2d1f2fb10) QEnterEvent(QPoint(29,23))
QWindowContainer(0x2a6c64a1000) QEnterEvent(QPoint(29,0))
QToolBar(0x2a6c64a0eb0) QEnterEvent(QPoint(30,21))
QComboBox(0x2a6c64a17e0) QEnterEvent(QPoint(23,12))
QWidgetWindow(0x2a6c89b5400, name = "QMainWindowClassWindow") QMouseEvent(MouseButtonPress, LeftButton, localPos=29.5,6.5, screenPos=669.5,286.5)
QComboBox(0x2a6c64a17e0) QFocusEvent(FocusIn, MouseFocusReason)
QWindowsVistaStyle(0x2a6c649d510, name = "windowsvista") QFocusEvent(FocusIn, MouseFocusReason)
QComboBox(0x2a6c64a17e0) QMouseEvent(MouseButtonPress, LeftButton, localPos=20,5, screenPos=669.5,286.5)
OpenGLWindow(0x2a6c649f610) QFocusEvent(FocusAboutToChange, OtherFocusReason)
OpenGLWindow(0x2a6c649f610) QFocusEvent(FocusOut, OtherFocusReason)
QWidgetWindow(0x2a6c89b5400, name = "QMainWindowClassWindow") QFocusEvent(FocusIn, OtherFocusReason)
QWidgetWindow(0x2a6c89b5400, name = "QMainWindowClassWindow") QMouseEvent(MouseButtonRelease, LeftButton, localPos=29.5,6.5, screenPos=669.5,286.5)
QComboBox(0x2a6c64a17e0) QMouseEvent(MouseButtonRelease, LeftButton, localPos=20,5, screenPos=669.5,286.5)
QComboBox(0x2a6c64a17e0) QFocusEvent(FocusAboutToChange, PopupFocusReason)
QComboBox(0x2a6c64a17e0) QFocusEvent(FocusOut, PopupFocusReason)
QWindowsVistaStyle(0x2a6c649d510, name = "windowsvista") QFocusEvent(FocusOut, PopupFocusReason)
QComboBoxListView(0x2a6c93deb90) QFocusEvent(FocusIn, PopupFocusReason)
QWindowsVistaStyle(0x2a6c649d510, name = "windowsvista") QFocusEvent(FocusIn, PopupFocusReason)
QWidgetWindow(0x2a6c94eb380, name = "QComboBoxPrivateContainerClassWindow") QEnterEvent(QPoint(20,9))
QComboBoxPrivateContainer(0x2a6d51a7c80) QEnterEvent(QPoint(20,9))
QComboBoxListView(0x2a6c93deb90) QEnterEvent(QPoint(19,8))
QWidget(0x2a6d503cc60, name = "qt_scrollarea_viewport") QEnterEvent(QPoint(19,8))
QWidgetWindow(0x2a6c94eb380, name = "QComboBoxPrivateContainerClassWindow") QMouseEvent(MouseButtonPress, LeftButton, localPos=17.5,15.5, screenPos=667.5,315.5)
QWidget(0x2a6d503cc60, name = "qt_scrollarea_viewport") QMouseEvent(MouseButtonPress, LeftButton, localPos=17,15, screenPos=667.5,315.5)
QWidgetWindow(0x2a6c94eb380, name = "QComboBoxPrivateContainerClassWindow") QMouseEvent(MouseButtonRelease, LeftButton, localPos=17.5,15.5, screenPos=667.5,315.5)
QWidget(0x2a6d503cc60, name = "qt_scrollarea_viewport") QMouseEvent(MouseButtonRelease, LeftButton, localPos=17,15, screenPos=667.5,315.5)
QComboBoxListView(0x2a6c93deb90) QFocusEvent(FocusAboutToChange, PopupFocusReason)
QComboBoxListView(0x2a6c93deb90) QFocusEvent(FocusOut, PopupFocusReason)
QWindowsVistaStyle(0x2a6c649d510, name = "windowsvista") QFocusEvent(FocusOut, PopupFocusReason)
QComboBox(0x2a6c64a17e0) QFocusEvent(FocusIn, PopupFocusReason)
QWindowsVistaStyle(0x2a6c649d510, name = "windowsvista") QFocusEvent(FocusIn, PopupFocusReason)

---> OpenGLWindow gets focus
OpenGLWindow(0x2a6c649f610) QEnterEvent(QPoint(28,14))
QWidgetWindow(0x2a6c89b5400, name = "QMainWindowClassWindow") QFocusEvent(FocusAboutToChange, OtherFocusReason)
QComboBox(0x2a6c64a17e0) QFocusEvent(FocusAboutToChange, OtherFocusReason)
QWidgetWindow(0x2a6c89b5400, name = "QMainWindowClassWindow") QFocusEvent(FocusOut, OtherFocusReason)
OpenGLWindow(0x2a6c649f610) QFocusEvent(FocusIn, OtherFocusReason)
QComboBox(0x2a6c64a17e0) QFocusEvent(FocusAboutToChange, OtherFocusReason)
QComboBox(0x2a6c64a17e0) QFocusEvent(FocusOut, OtherFocusReason)
QWindowsVistaStyle(0x2a6c649d510, name = "windowsvista") QFocusEvent(FocusOut, OtherFocusReason)
OpenGLWindow(0x2a6c649f610) QMouseEvent(MouseButtonPress, LeftButton, localPos=33.5,31, screenPos=673.5,334)
OpenGLWindow(0x2a6c649f610) QMouseEvent(MouseButtonRelease, LeftButton, localPos=33.5,31, screenPos=673.5,334)
OpenGLWindow(0x2a6c649f610) QKeyEvent(KeyPress, Key_D, text="d")
OpenGLWindow(0x2a6c649f610) QKeyEvent(KeyRelease, Key_D, text="d")
OpenGLWindow(0x2a6c649f610) QKeyEvent(KeyPress, Key_Alt, AltModifier)

1) With pointer handling:
=========================

"5.12.0 windows" ()
Qt::StrongFocus
QWidgetWindow(0x204c1116b40, name = "QMainWindowClassWindow") QFocusEvent(FocusIn, OtherFocusReason)
QWindowContainer(0x204be9b6450) QFocusEvent(FocusIn, ActiveWindowFocusReason)
QWindowsVistaStyle(0x204be998440, name = "windowsvista") QFocusEvent(FocusIn, ActiveWindowFocusReason)
QWidgetWindow(0x204c1116b40, name = "QMainWindowClassWindow") QFocusEvent(FocusAboutToChange, OtherFocusReason)
QWindowContainer(0x204be9b6450) QFocusEvent(FocusAboutToChange, OtherFocusReason)
QWidgetWindow(0x204c1116b40, name = "QMainWindowClassWindow") QFocusEvent(FocusOut, OtherFocusReason)
OpenGLWindow(0x204be9b3910) QFocusEvent(FocusIn, OtherFocusReason)
QWindowContainer(0x204be9b6450) QFocusEvent(FocusAboutToChange, OtherFocusReason)
QWindowContainer(0x204be9b6450) QFocusEvent(FocusOut, OtherFocusReason)
QWindowsVistaStyle(0x204be998440, name = "windowsvista") QFocusEvent(FocusOut, OtherFocusReason)
OpenGLWindow(0x204be9b3910) QEnterEvent(QPoint(108,51))
QWidgetWindow(0x204c1116b40, name = "QMainWindowClassWindow") QEnterEvent(QPoint(3,10))
QMainWindow(0xd8581ef920) QEnterEvent(QPoint(3,10))
QToolBar(0x204be9b7170) QEnterEvent(QPoint(3,10))
QComboBox(0x204be9b6370) QEnterEvent(QPoint(33,11))
QComboBox(0x204be9b6370) QEnterEvent(QPoint(47,6))
QComboBox(0x204be9b6370) QEnterEvent(QPoint(10,10))
QWidgetWindow(0x204c1116b40, name = "QMainWindowClassWindow") QMouseEvent(MouseButtonPress, LeftButton, localPos=30.5,13, screenPos=670.5,293)
QComboBox(0x204be9b6370) QFocusEvent(FocusIn, MouseFocusReason)
QWindowsVistaStyle(0x204be998440, name = "windowsvista") QFocusEvent(FocusIn, MouseFocusReason)
QComboBox(0x204be9b6370) QMouseEvent(MouseButtonPress, LeftButton, localPos=21,11, screenPos=670.5,293)
OpenGLWindow(0x204be9b3910) QFocusEvent(FocusAboutToChange, OtherFocusReason)
OpenGLWindow(0x204be9b3910) QFocusEvent(FocusOut, OtherFocusReason)
QWidgetWindow(0x204c1116b40, name = "QMainWindowClassWindow") QFocusEvent(FocusIn, OtherFocusReason)
QWidgetWindow(0x204c1116b40, name = "QMainWindowClassWindow") QMouseEvent(MouseButtonRelease, LeftButton, localPos=30.5,12, screenPos=670.5,292)
QComboBox(0x204be9b6370) QMouseEvent(MouseButtonRelease, LeftButton, localPos=21,10, screenPos=670.5,292)
QComboBox(0x204be9b6370) QFocusEvent(FocusAboutToChange, PopupFocusReason)
QComboBox(0x204be9b6370) QFocusEvent(FocusOut, PopupFocusReason)
QWindowsVistaStyle(0x204be998440, name = "windowsvista") QFocusEvent(FocusOut, PopupFocusReason)
QComboBoxListView(0x204c1843910) QFocusEvent(FocusIn, PopupFocusReason)
QWindowsVistaStyle(0x204be998440, name = "windowsvista") QFocusEvent(FocusIn, PopupFocusReason)
QWidgetWindow(0x204c1116b40, name = "QMainWindowClassWindow") QEnterEvent(QPoint(21,-8))
QWidgetWindow(0x204cdd71160, name = "QComboBoxPrivateContainerClassWindow") QEnterEvent(QPoint(18,0))
QComboBoxPrivateContainer(0x204cde5dfa0) QEnterEvent(QPoint(18,0))
QComboBoxListView(0x204c1843910) QEnterEvent(QPoint(17,0))
QWidget(0x204c199da00, name = "qt_scrollarea_viewport") QEnterEvent(QPoint(17,0))
QWidgetWindow(0x204cdd71160, name = "QComboBoxPrivateContainerClassWindow") QMouseEvent(MouseButtonPress, LeftButton, localPos=15,8, screenPos=665,308)
QWidget(0x204c199da00, name = "qt_scrollarea_viewport") QMouseEvent(MouseButtonPress, LeftButton, localPos=14,7, screenPos=665,308)
QWidgetWindow(0x204cdd71160, name = "QComboBoxPrivateContainerClassWindow") QMouseEvent(MouseButtonRelease, LeftButton, localPos=15,8, screenPos=665,308)
QWidget(0x204c199da00, name = "qt_scrollarea_viewport") QMouseEvent(MouseButtonRelease, LeftButton, localPos=14,7, screenPos=665,308)
QComboBoxListView(0x204c1843910) QFocusEvent(FocusAboutToChange, PopupFocusReason)
QComboBoxListView(0x204c1843910) QFocusEvent(FocusOut, PopupFocusReason)
QWindowsVistaStyle(0x204be998440, name = "windowsvista") QFocusEvent(FocusOut, PopupFocusReason)
QComboBox(0x204be9b6370) QFocusEvent(FocusIn, PopupFocusReason)
QWindowsVistaStyle(0x204be998440, name = "windowsvista") QFocusEvent(FocusIn, PopupFocusReason)
OpenGLWindow(0x204be9b3910) QEnterEvent(QPoint(25,5))
OpenGLWindow(0x204be9b3910) QMouseEvent(MouseButtonPress, LeftButton, localPos=65.5,39, screenPos=705.5,342)
OpenGLWindow(0x204be9b3910) QMouseEvent(MouseButtonRelease, LeftButton, localPos=65.5,39, screenPos=705.5,342)
QWidgetWindow(0x204c1116b40, name = "QMainWindowClassWindow") QKeyEvent(KeyPress, Key_D, text="d")
QComboBox(0x204be9b6370) QKeyEvent(KeyPress, Key_D, text="d")
QWidgetWindow(0x204c1116b40, name = "QMainWindowClassWindow") QKeyEvent(KeyRelease, Key_D, text="d")
QComboBox(0x204be9b6370) QKeyEvent(KeyRelease, Key_D, text="d")
QToolBar(0x204be9b7170) QKeyEvent(KeyRelease, Key_D, text="d")
QMainWindow(0xd8581ef920) QKeyEvent(KeyRelease, Key_D, text="d")
QWidgetWindow(0x204c1116b40, name = "QMainWindowClassWindow") QKeyEvent(KeyPress, Key_Alt, AltModifier)
QComboBox(0x204be9b6370) QKeyEvent(KeyPress, Key_Alt, AltModifier)
QToolBar(0x204be9b7170) QKeyEvent(KeyPress, Key_Alt, AltModifier)
QMainWindow(0xd8581ef920) QKeyEvent(KeyPress, Key_Alt, AltModifier)
QComboBox(0x204be9b6370) QFocusEvent(FocusAboutToChange, ActiveWindowFocusReason)
QComboBox(0x204be9b6370) QFocusEvent(FocusOut, ActiveWindowFocusReason)
QWindowsVistaStyle(0x204be998440, name = "windowsvista") QFocusEvent(FocusOut, ActiveWindowFocusReason)

^^^^^ OpenGLWindow does not get focus any more.