This is described in "Why can I only make something with Scratch or Python for my machine learning project?" in the FAQs at
https://machinelearningforkids.co.uk/help
In short, App Inventor support hasn't been disabled or removed - it's just that it's only ever been presented as an option for projects where the machine learning model has been trained in the cloud. I'm assuming that you've instead trained a model on your computer, which is why you're not seeing it as an option.
Kind regards
D