I've successfully configured LDAP users and groups on Proxmox 6.3-6 and that works fine. I can login with an LDAP user and I've given one of the LDAP groups (admins) full privileges just like the built in root@PAM user. They look identical when I view their permissions in the Users tab. Everything appears to be available, except that the LDAP user can't edit the Features option of an LXC container. Everything else, yes, but not that one setting. The root@PAM user can, however, so it's just something not consistent between the two, but they both are Administrator roles so I would think there's nothing that the LDAP user can't do that root@PAM can.