I've ported an existing Flutter app over to MacOS using flutter-desktop-embedding, and when doing a test upload to the Mac App Store to verify the release process for when things eventually get stable enough to do a release, the upload is rejected due to the underscore in the bundle identifier of FlutterEmbedder.framework.

Removing the underscore from the bundle identifier in the Info.plist of FlutterEmbedder.framework and in FLEViewController.m allows a successful upload.