I'm having the same problem - I am a gui admin (not the IT admin) and I can create a group, but there is no way to add members to it. Is there no way for me to modify the group I created? We use Okta SSO.
I have also read the admin guide, and none of the situations seem to match, as there IS a groups tab, and I AM shown as the owner.
edit: doh, I always forget that the admin guide built into the server is not always the current one