Hi, I have over 90 educational apps published and this morning (August 10th) I encountered the same problem. Google play now requires API Level 31. We've been through this before, especially when they stopped accepting APK and started requiring AAB. There are options to try to generate the AAB File on the KODULAR Platform. Just import your AIA file on that platform, but I believe they are also using API Level 30 there. I suggest waiting for the update of the great platform, APP INVENTOR.
I hope I was helpfull.