This has been moved as an example in the Flame repository: https://github.com/flame-engine/flame/tree/main/examples/lib/stories/games/trex
The joy of our offline hours recreated with Flutter and Flame
https://medium.com/@renancaraujo/creating-the-t-rex-game-with-flutter-and-flame-6d01add1ad5b