I want to make my NavigationBar transparent. I have tried extendBody: true on Scafold with surfaceTintColor=Colors.transparent to the NavigationBar widget, but nothing changed.

How to create a transparent Material 3 NavigationBar in Flutter?
According to the document, SurfaceTintColor is the color of the surface tint overlay applied to the app bar's background color to indicate elevation.
If you want to make the AppBar transparent, just use the property backgroundColor instead.
Scaffold(
      extendBody: true,
      backgroundColor: Colors.white,
      appBar: AppBar(
        backgroundColor: Colors.transparent, // To make appBar transparent
        
        /// This is not necessary. You can play around 
        /// to see surfaceTintColor when the AppBar is transaprent
        surfaceTintColor: Colors.redAccent,
        elevation: 3,
        title: Text(widget.title),
      ),
),

It is also applied to NavigationBar
bottomNavigationBar: NavigationBar(
        surfaceTintColor: Colors.amber, // not neccessary
        backgroundColor: Colors.transparent,
        destinations: [
          Icon(Icons.book, color: Colors.blue,),
          Icon(Icons.map, color: Colors.blue,),
        ],
      ),

