QWidget::restoreGeometry does not work as documented.

class MyTest : public QMainWindow
{
  public:
    MyTest() : QMainWindow()
    {
      QSettings settings(QStringLiteral("org"), QStringLiteral("test"));
      settings.beginGroup(QStringLiteral("GROUP"));
      restoreGeometry(settings.value(QStringLiteral("GEOMETERY"), QByteArray()).toByteArray());
      restoreState(settings.value(QStringLiteral("STATE")).toByteArray());
      settings.endGroup();
    }
    void closeEvent(QCloseEvent *event) override
    {
      QSettings settings(QStringLiteral("org"), QStringLiteral("test"));
      settings.beginGroup(QStringLiteral("GROUP"));
      settings.setValue(QStringLiteral("GEOMETERY"), saveGeometry());
      settings.setValue(QStringLiteral("STATE"), saveState());
      settings.endGroup();
    }
};

int main(int argc, char *argv[])
{
  QApplication app(argc, argv);
  MyTest mainWin;
  mainWin.show();
  return QApplication::exec();
}