Reasons for force remove could be a very rare scenario such as existing vCenter has been either rebuilt with new IP or the vCenter is no longer available.
Registering new vCenter may fail with below error as the Protected site might still be associated with the Old vCenter in the backend.
HTTP 500: Failed to connect to the vCenter server.
How to manually remove a vCenter from a protected site.
vcenter remove --site-id <site_id> --vcenter <VCENTER IP>
Engage VMware by Broadcom Support for removal of the vCenter from the backend Cloud Filesystem and Orchestrator. Please provide the vCenter IP to be removed and the site id