An open-source production-quality starter app for Flutter with code available at https://github.com/gregertw/actingweb_firstapp. It's functionality is fairly basic with appauth (demo.identityserver.io) based account management and login and a main screen that shows you the stream of location coordinates and allows you to show a Google Maps of your location. It also has a drawer menu with various options and logout. However, the code base offers a fairly complete set of things you would need to develop and maintain a production-quality app. See https://stuff.greger.io/2019/07/production-quality-flutter-starter-app.html for more details.
