Comment by throw0101a

> NAT provides security because normally it disallows external actors on the outside from accessing resources on the inside side.

Which NAT?

A 1:1 'basic' NAT [1] could allow stateless flow between two different address schemes. Then you have NAPT where multiple IPs can be mapped via one-IP-many-port system, in which you need state and thus have a filtering mechanism.

Similarly you can have IPv6 ULA and do a stateless address translation (NPT) without any blocking policy, which would achieve the same (lack of) security as the 1:1 scenario above.

Address translation can have the same level (or not) of security in both IPv4 and IPv6.

[1] https://datatracker.ietf.org/doc/html/rfc2663#section-4.1.1