This happens with both the Flutter and the Android Onfido SDKs on any version: oldest to newest; they all behave in exactly the same way. I'll use Flutter 8.4.0 as the example for my case. this is what I call to render the Onfido workflow. It works, all of the content works and the user can go through the process:

final Onfido onfido = Onfido(  
  sdkToken:  
  sdkToken,  
  nfcOption: NFCOptions.DISABLED,  
  onfidoTheme: OnfidoTheme.DARK,  
  iosAppearance: IOSAppearance(  
    buttonCornerRadius: 4,  
  ),  
);  
await onfido.startWorkflow(workflowRunId);

The problem is that only on Android; it is entirely impossible to navigate back away from this page. There is no on-screen back (up) button, no Toolbar is displayed, and the Android device back button doesn't do anything. This means that the only way to dismiss the flow is by killing the app and reopening it. The same workflow on iOS renders an on screen back button which works, but on Android, whether via the Flutter SDK or by using the Android SDK directly, there's just no way out of the screen once it's open (unless you complete the entire flow).

The Flutter and Android sample apps both have the same issue too.

There is no documentation that says anything about a back button and I don't understand how to fix this issue. Does anyone here have any experience with this?

Calling start() and providing Flowsteps rather than startWithWorkflow does show a back button. The workflow can change based on various things happening in the backend so that flow wouldn't be appropriate for our use case.