I have an app that is by design always limited to DeviceOrientation.portraitUp. We don't allow any other orientations except for one screen, which is used as PDF or Image viewer, I want to allow ONLY this view to rotate freely. It works fine on Android but not on iOS.

I have added this in initState:
SystemChrome.setPreferredOrientations([DeviceOrientation.portraitUp, DeviceOrientation.landscapeRight, DeviceOrientation.landscapeLeft]);

in that case, all good on Android, but no effect on iOS it's like it has only DeviceOrientation.portraitUp

if I do:

if (Platform.isIOS) {
      SystemChrome.setPreferredOrientations([DeviceOrientation.landscapeRight, DeviceOrientation.landscapeLeft]);
    }

That allows landscape rotations but I cannot do portrait...

Any ideas?

Not mentioned but I do do:

void dispose() {
    SystemChrome.setPreferredOrientations([DeviceOrientation.portraitUp]);
    super.dispose();
  }