Upon navigating to Administration > Control Panel > Trusted Certificates, an expiration warning is visible for the LDAP authentication source certificate.
VMware Aria Operations 8.18.5
When configured with LDAP as an authentication source, VMware Aria Operations utilizes a Trust on First Use (TOFU) mechanism to ingest the server's certificate. Because these certificates carry a specific validity period, the system will trigger a warning notification as the expiration date approaches to prevent authentication failures.
Review article Certificate overview for VMware Aria Operations section 'Adapter and authentication sources' for more information on endpoint certificates and potential caveats.