One of the happiest development choices I've made is learning Flutter. Instead of developing separate Android and iOS apps now, I just make one Flutter app and compile it down to native code for both platforms. For that reason, I'm not actively maintaining my old Android and iOS answers, so feel free to make updates to them yourself, even to the code (preferably testing that your changes work). I am trying to maintain my Flutter answers, so please leave a comment when you find a mistake or shortcoming.
My Flutter and Dart articles