I'll start by saying I'm not very familiar with Avamar... I built a new vCenter 6.7u2 environment added a v19 proxy to it and then associated the proxy with our Avamar server.
When I go into Policy Management \ Groups then create a new Backup Group I do not see any VMs under "vcenter 6.7 \ Members \ Container Clients".
I do see VMs under "vcenter 6.0 \ Members \ Container Clients".
I'm probably missing something really basic.
**EDIT: I found out that I had to add the clients via the Administration tool.