mkdir -p android/app/src/main/assets
react-native bundle --platform android --dev false --entry-file index.js --bundle-output android/app/src/main/assets/index.android.bundle --assets-dest android/app/src/main/res
cd android && ./gradlew assembleRelease -x bundleReleaseJsAndAssets

- Your APK will be present in the folder
/android/app/build/outputs/apk/release