You want to know the internals of a running Flutter app

Use Dart Observatory provided by Dart SDK.

Dart Observatory is a tool provided by Dart SDK to profile and debug Dart applications
Observatory is an important tool for debugging, tracing, and profiling Flutter apps.

View an app’s CPU profile.
View an app’s memory allocation profile
Debug an app interactively.
View snapshots of an app’s heap.
View logs generated by an app.

When a Flutter app is started using flutter run, Observatory is also started and waiting for connections.

Navigate to the URL in the browser and you can see the UI of Observatory

https://dart-lang.github.io/observatory/

Changes to the app’s main() method may only be reflected after a hot restart.