Creating a Governance > Policy for Resource Type, Azure - Savings Plans, the only option is for Configuration - Missing Tags. Where a policy for Azure - Reservation also includes a second rule for Usage - Expiring Reservations.
Our Product team is aware that currently there is no alerting functionality for when an Azure Savings Plan is expiring. Please reach out to your Account Team to discuss this topic and highlight your need for this alerting functionality. Additionally you can open a support ticket to request information and add your interest for this functionality.