I created a new project by running flutter create .. Then I modified the Android app's package by modifying it in:

Now it built fine, but it got stuck in the assembleGradle step. I ended up on https://stackoverflow.com/questions/59516408/flutter-app-stuck-at-running-gradle-task-assembledebug. In some of the posters' cases, gradle downloaded at really low speed. I don't think it was the case for me, but I learned one thing. How to run it in verbose mode: flutter run -v.