Hi,
It's a warning reported on a cluster or a ESXi hosts which you are trying to update. DRS should be enabled on the cluster, so it can migrate VMs including vCenter VM to update and reboot them.
Please refer 'Host issues' in this document for more info --> Remediation Pre-Check Report
If you do not have a cluster, ensure vCenter VM is registered to another ESXi host before remediating the host where it is currently running.
I hope that helps
