For more information, see the public issue.

Build an app bundle

This section describes how to build a release app bundle.
If you completed the signing steps,
the app bundle will be signed.
At this point, you might consider obfuscating your Dart code
to make it more difficult to reverse engineer. Obfuscating
your code involves adding a couple flags to your build command,
and maintaining additional files to de-obfuscate stack traces.

From the command line:

Enter cd [project]

Run flutter build appbundle
(Running flutter build defaults to a release build.)

The release bundle for your app is created at
[project]/build/app/outputs/bundle/release/app.aab.