Sorry for the issue you are facing with alerts in SQL MI. Seems like this is not a bug after checking internally. I believe that was a misunderstanding from my end.
After going through the following docs, the error number you would like to create alerts on is not supported in Azure SQL MI.
I would suggest raising this feature request at https://feedbackportal.microsoft.com/feedback/search/?q=azure+sql
Sorry for any inconvenience this may have caused.
Regards,
Oury