You need to use the versions of Scratch that are provided by the Machine Learning for Kids site. They can be launched by clicking the Scratch, or 'Scratch 3', buttons from your project page.
The version of Scratch at
https://machinelearningforkids.co.uk/scratch3/ has been modified to add support for the artificial intelligence capabilities. This means that ML projects need to be opened in the version of Scratch at
https://machinelearningforkids.co.uk/scratch3/
Kind regards
D