The inability to relocate a Content Library directly is due to how vSphere manages library data:
The library’s files (OVF, OVA, ISOs, etc.) reside on the backing datastore.
The library’s metadata is stored in the vCenter Server Database (VCDB).
vSphere lacks a built-in feature to change the backing datastore for an existing Content Library, requiring manual intervention for migration
VMware vSphere ESXi 7.x
VMware vSphere ESXi 8.x
Migrating content library datastore is a new product feature released in vsphere 9, up until this version it is not possible to migrate the content library.
Upgrade to vSphere 9 to utilize the new feature.
https://techdocs.broadcom.com/us/en/vmware-cis/vsphere/vsphere/9-0/how-do-i-migrate-a-content-library-to-another-datastore.html