Hi Anthony,
Starting in 2.3.7.x we introduce event notifications for certificates expiring in the Catalyst Center (formerly known as Cisco DNA Center). Currently 2.3.7.5 is available for limited access through our Canary/FCS program that requires submitting an access form and approval. 2.3.7.6 should be the first generally available release and this is slated to come out towards the end of July to mid August area.
The events that you can subscribe to are for the internal maglev/MKS certs expiring and/or when the system (SSL) certificate is withing 90 days of expiring.