NAT66 does not yet support groups as NAT does (reported in https://forum.vyos.io/t/nat66-destination-group-not-available/15139/1)
set nat destination rule 10 destination Possible completions: address IP address, subnet, or range > group Group port Port number
set nat66 destination rule 10 destination Possible completions: address IPv6 address or prefix to be translated port Port number