Hi @Anonymous ,
I tested it on my side and the trigger works fine.

Please make sure that the alert rule(Alert Id) you selected has not been deleted and that the corresponding tile has not been deleted.
In addition you could try to recreate such a Flow and update the connection.
Previously, other users have encountered similar problems with "Unable to check new events. View details". Re-creating Flow is a workaround that can be used.
Please take a try and see if issue still exists.
Best Regards,