QWebView.showFullScreen() does not work well with QPA LinuxFB

Our application simply invokes QWebView.show()[or showFullScreen()) to display a local webpage and therefore there is not much room for error.

For Wayland QPA (real window system), both QWebView.show() and QWebView.showFullScreen() work accordingly.
For EGLFS (Full Screen system), both QWebView.show() and QWebView.showFullScreen() display full-screen as they should.
For LinuxFB (which is neither window-system, nor full-screen), both QWebView.show() and QWebView.showFullScreen( ) active like show(),
i.e., non-full-screen system.

There is no other QT5 web browser demo application which uses QWebView directly, instead, QMainWindow is used and the application works fine in LinuxFB.