From August 1st you can only send apks to Google Play for apps already there. For new apps you can only upload AAB. You shouldn't use the test server for sending aabs to Google Play yet, only if you want to experiment with the new functions not for production apps.
It means you cannot publish your new app on Google until MIT releases version nb187 of App Inventor 2.
There are still numerous bugs. It was hoped to launch 1 August. When will it be available? When MIT fixes the bugs.