Add-to-app flows with Android Studio are only supported on
Android Studio 3.6 with version 42+ of the Flutter plugin
for IntelliJ. The Android Studio integration also only
supports integrating using a source code Gradle subproject,
rather than using AARs. See below for more details on
the distinction.

Using the File > New > New Module… menu in
Android Studio in your existing Android project,
you can either create a new Flutter module to integrate,
or select an existing Flutter module that was created previously.

If you create a new module, you can use a wizard to
select the module name, location, and so on.

The Android Studio plugin automatically configures your
Android project to add your Flutter module as a dependency,
and your app is ready to build.

Note:
  To see the changes that were automatically made to your
  Android project by the IDE plugin, consider using
  source control for your Android project before performing
  any steps. A local diff shows the changes.