Just to rule out licensing issues. Can you confirm that you have a vCenter Server Standard license, i.e. no Essentials, or Foundation license.
From https://docs.vmware.com/en/VMware-vSphere/6.7/com.vmware.vsphere.avail.doc/GUID-8FD87389-8CC9-4298-8...
--> "vCenter HA requires a Standard license"
André
