When trying to configure vCenter HA it fails with the message 'The request refers to an unexpected or unknown type vcenter'
This happens in vsphere 6.7 3h build 16275304 (but presumably also in other versions)
First I thought it was my portgroup type settings, I use ephemeral portgroups for high priority servers as the vCenter.
But the cause of this issue is selecting a storage DRS cluster instead of a datastore.
You don't get an error or warning when selecting a sDRS cluster for your storage location, but the warning pop ups when clicking on 'Next' after configuring the portgroups for each vCenter node.
A bit confusing.
When using storage drs clusters, first select a datastore instead of a storage cluster as your destination.
And then when the wizard successfully finished its job, create sDRS VM anti-affinity rule for the three vCenter VMs.