Adding a watch app to a Flutter iOS application

looks like apple watch development is supported in flutter now. here is an example:

https://github.com/magnatronus/flutter-watchtips

Flutter doesn't support Apple Watch apps due to the fact that it lacks Bitcode support for iOS as discussed in this GitHub issue.

You can track the state of Adding Bitcode support for iOS - Flutter GitHub issue, but currently it seems to have a low priority for the Flutter development team.