The following method is for unsubscribing a local content library from a publisher content library due to plans of decommission the vCenter where the content library is subscribed.
VMware vCenter Server 8.x
Before proceeding with the resolution, take a snapshot of the vCenters to be safe (ONLINE snapshot for standalone vCenter and OFFLINE snapshot for ELM or Linked Mode vCenters).
Content library > Delete subscription of a published library on the libraryContent Libraries list.Subscriptions tab, select one or multiple subscriber libraries from the list.Delete subscription button to delete the selected subscriber libraries.The subscription is deleted and you cannot use the publish function to synchronize.