An alarm in the vSphere Client UI shows that a certificate in the VMware Endpoint Certificate Store (VECS) and gives a KB link to follow.
VMware vCenter Server 8.x
This alarm is raised when there are certain number of days (customizable, but default is 30days) until the MACHINE_SSL_CERT certificate expires.
Use the vCert script to replace the MACHINE_SSL_CERT
Ensure that you have offline snapshots of the vCenter Server, and if applicable, all linked vCenter Server nodes before replacing certificates.
VMware vCenter in Enhanced Linked Mode pre-changes snapshot (online or offline) best practice