Note:
  As of Flutter 2.5, the launch and splash screens have been
  consolidated—Flutter now only implements the Android launch screen,
  which is displayed until the framework draws the first frame.
  This launch screen can act as both an Android launch screen and an
  Android splash screen via customization, and thus, is referred to
  as both terms. For example of such customization, check out the
  Android splash screen sample app.

If, prior to 2.5, you used flutter create to create an app,
  and you run the app on 2.5 or later, the app might app crash.
  For more info, see the Deprecated Splash Screen API Migration guide.

Note:
  For apps that embed one or more Flutter screens within an
  existing Android app, consider
  pre-warming a FlutterEngine and reusing the
  same engine throughout your app to minimize wait
  time associated with initialization of the Flutter engine.

Initializing the app