App Inventor 2 apps cannot use or create the Android App Bundle to ‘optimize’ your app. You have to do that yourself by re-using components etc.
Please read the articles in the Forum to learn the details about how to handling this isssue using AI2:
https://groups.google.com/forum/#!searchin/mitappinventortest/app$20bundle|sort:date
What do you do? Just ignore the warning. An App Bundle is not a requirement. Just upload your app as it is.
Regards,
Steve