Option 1

1_start_of_app.dart

class MyApp extends ConsumerWidget {
  @override
  Widget build(BuildContext ctx, WidgetRef ref) =>
      ref.watch(settingsAsyncProvider).when(
            loading: () => RowLoading(),
            error: (e, s) => CustomError(body: '$e \n \n $s'),
            data: (data) {
              return MaterialApp(
                title: 'MyApp',
                localizationsDelegates: AppLocalizations.localizationsDelegates,
                supportedLocales: AppLocalizations.supportedLocales,
                theme: ThemeData(primaryColor: PrimaryColor),
                locale: ref.watch(localeProvider),
                home: HomePage(settings: data),
              );
            },
          );
}

2_settingsAsyncNotifier.dart

@riverpod
class SettingsAsyncNotifier extends AsyncNotifier<Settings> {
  Future<Settings> _readSettings() async =>
      await DataController.fileDB.processSettingsFile();

  @override
  FutureOr<Settings> build() async => _readSettings();
    
  Future<void> set(Settings settings) =>
      update((state) => settings);

  Future<void> writeSettings(Settings settings) async {
    // settings object is already modified, just need to be written
    state = const AsyncValue.loading();
    state = await AsyncValue.guard(() async {
      await DataController.fileDB.writeSettingsFile(settings);
      return settings; // already modified object
    });
  }
}

final settingsAsyncProvider =
    AsyncNotifierProvider<SettingsAsyncNotifier, Settings>(() {
  return SettingsAsyncNotifier();
});

3_inkwell_saving_settings.dart

InkWell(
    child: Icon(Icons.check, size: 32, color: Colors.white70),
    onTap: ()  => ref.read(settingsAsyncProvider).writeSettings(_controller.settings)
),