It is possible to use flutter to create something to Watch OS or Android Wear?

At the moment, neither watchOS, nor Android Wear is supported by Flutter.

The lack of watchOS support is due to the lack of 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.

For Android Wear, there seems to be no official reasons, but it is still not supported. You can track the progress of that in this GitHub issue.