[REG.]Widgets lose their focus frame when QProxyStyle is set

If a QProxyStyle (or derived class) is set on QApplication, some widgets (QPushButton, QCheckBox) no longer have a focus frame when they are focused (on macOS).

With Qt 6.3.2, or if the style is directly set on the widget everything is ok.

I guess the problem was introduced with this commit:

https://code.qt.io/cgit/qt/qtbase.git/commit/?id=5d8a7652b995124495ef4f4a43fd8cf461367d62

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    // as soon as QProxyStyle (or derived class) is set on QApplication
    // some widgets no longer have a focus ring
    a.setStyle(new QProxyStyle);

    QWidget *w = new QWidget;
    w->setLayout(new QHBoxLayout(w));
    w->layout()->addWidget(new QPushButton("PushButton", w));
    w->layout()->addWidget(new QCheckBox("CheckBox", w));
    w->show();

    return a.exec();
}

Important note:

Keyboard navigation is disabled on macOS by default. You have to enable it, otherwise buttons won't get focused at all when pressing TAB.

macOS 13: System Settings -> Keyboard -> Keyboard navigation

macOS <=12: System Settings -> Keyboard -> Shortcuts -> Use keyboard navigation to move focus...