NAT is more like the add-on that most network operators don’t decide to employ for IPv6-only networks anymore, but NAT by itself is not part of IPv4. You can NA

NAT is more like the add-on that most network operators don’t decide to employ for IPv6-only networks anymore, but NAT by itself is not part of IPv4. You can NAT IPv6 networks perfectly fine - but for IPv4 it is often a necessary evil when private network ranges overlap or you need to represent a single IP to the outside world.