It's because that app might have splitTypes parameter. If the app has splitTypes parameter there will be more than one apks built and required and you can't just simply share the app to telegram from your phone and decompile it. It won't be full, when you share apk from your phone it extracts base.apk and sends it anywhere you want. In order to get libflutter.so you would need arm64_v8a.apk and you will need all split apks to decompile normally and make it work after recompiling.