How to add Loading Spinner to Layout Builder with out having the screen flicker?

Question

I am working on an app with layoutbuilder and i have different visuals of the app i want to show when the user goes from portrait to landscape mode a spinner should display and after 2 seconds that spinner should vanish.

I got the functionality to work i have used ( WidgetsBinding.instance.addPostFrameCallback((_) { )), but every time I change the orientation the loading spinner comes and then after it goes away my screen flickers and does not stop flickering or flashing

I understand the reason is that the loading spinner is showing and then my other widgets are rebuilding, but I have a format which I need all to be Stateful widget, unless someone has another idea?

1. user changes portrait to landscape
2. spinner displays for 2 seconds
3. user sees screen in landscape.

Loadingshimmer is the class with the loader singlechildscrollview is landscape mode...

bool loading = false; 

       child: LayoutBuilder(builder: (context, constraints) {
              if (constraints.maxWidth > 600 && constraints.maxHeight < 1000) {
         WidgetsBinding.instance.addPostFrameCallback((_) {       
                  setState((){
                loading = true;
});
});
                Timer(Duration(seconds: 1), () {
                setState(() {
                loading = false;
               
                 });
                });
    
                // child: OrientationBuilder(
                //   builder: (BuildContext context, Orientation orientation) {
                // if (orientation == Orientation.portrait) {
                // (constraints.maxWidth > 600) {
                print(height);
                print(width);
                return loading
                    ? LoadingShimmer()
                    : SingleChildScrollView(