MIT hoped to have the Android api 31 update by the end of August. It will be deployed and available whenever the software receives approval from Google and the release is ready.
When the software is updated, you will find a notice here Release Notes for MIT App Inventor 2 .
There are alternatives to waiting for the official release:
Try Anke's advice Target API level 31 - #9 by Anke
Code your commercial apps in Android Studio or Delphi Community Edition, or B4A instead of a great compiler intended principally for educational purposes and experimentation.
MIT makes ever effort to make App Inventor available for all developers as soon as possible. Sometimes its self imposed goals and deadlines are delayed.