Code Improvements

[YukiAttano]

I have some suggestions to improve the generated code:

First:

class F {
  static Flavor? appFlavor;

  static String get name => appFlavor?.name ?? '';

...
}

can be rewritten to a non null final variable
(because it is (and probably must only be) set at app start

class F {
  static late final Flavor appFlavor;

  static String get name => appFlavor.name;

...
}

Second:

 Widget _flavorBanner({
    required Widget child,
    bool show = true,
  }) =>
      show
          ? Banner(
        child: child,
        location: BannerLocation.topStart,
        message: F.name,
        color: Colors.green.withOpacity(0.6),
        textStyle: TextStyle(
            fontWeight: FontWeight.w700,
            fontSize: 12.0,
            letterSpacing: 1.0),
        textDirection: TextDirection.ltr,
      )
          : Container(
        child: child,
      );

Not just that the Container surrounding the child can be removed and the child parameter of the Banner should go last, you can improve your code by replacing the "if else" with a visibility.

(Also note: instead of using a function, it is highly recommended to use a Widget class instead)

 Widget _flavorBanner({
    required Widget child,
    bool show = true,
  }) {
    return Visibility(
      replacement: child,
      visible: show,
      child: Banner(
        location: BannerLocation.topStart,
        message: F.name,
        color: Colors.green.withOpacity(0.6),
        textStyle: TextStyle(fontWeight: FontWeight.w700, fontSize: 12.0, letterSpacing: 1.0),
        textDirection: TextDirection.ltr,
        child: child,
      ),
    );
  }