Comment by zamadatix

What they're saying is NAT66 on Fortigates is 1:1 NAT, i.e. prefix translation, not n:1 NAPT, i.e. address+port translation.

I can't imagine why one would ever intend to use NAPT over NAT when the addresses were available though (e.g. on IPv4 where having a minimum of 2^64 public addresses per connection is not assumed), which is the only reason I wouldn't expect anyone to have bothered implementing it. So sure, it's what people refer to on IPv4, but it's not materially different from 1:1 NAT or necessarily adding any additional value.