Hi Henry, You need to replace the entire UI with Flutter code in Dart programming language - flutter.dev/docs/get-started/flutter-for/android-… and for REACT you need to write first in React Native with using your own view - medium.com/47billion/how-to-develop-android-ui-co… and then migrate it to Android APK.

Hope this answers your question.

You can read this blog to better understand these 2 frameworks - simform.com/react-native-vs-flutter