How to switch loading indicator as default base on device ( Andriod show circularprogressindicator and IOS show CupertinoActivityIndicator)?

You can do that by creating your own widget. Flutter does it for BackButtonIcon widget.

I just got the code from it and modifying it for you to use :) All you need to do is to use LoadingIndicator() where you need it.

class LoadingIndicator extends StatelessWidget {
  const LoadingIndicator({Key? key}) : super(key: key);

  /// Returns the appropriate "loading indicator" icon for the given `platform`.
  Widget _getIndicatorWidget(TargetPlatform platform) {
    switch (platform) {
      case TargetPlatform.iOS:
      case TargetPlatform.macOS:
        return const CupertinoActivityIndicator();
      case TargetPlatform.android:
      case TargetPlatform.fuchsia:
      case TargetPlatform.linux:
      case TargetPlatform.windows:
      default:
        return const CircularProgressIndicator();
    }
  }

  @override
  Widget build(BuildContext context) =>
      _getIndicatorWidget(Theme.of(context).platform);
}