To spell that out a bit more - a ULA to NPT address is IP based and not port based and is way more useful.
When you do a IPv4 "pinhole" port map you get precisely one mapping and it will timeout eventually, which can lead to all sorts of exciting debugging opportunities.
IPv4 does have 1:1 NAT but there are so few IPs so whilst I have a /24, 2 x /28 and 2 x /29 to play with and others, I doubt most do.
NPTv6 maps an entire address space from A->B and is actually not designed to deal with NATv4 anyway. It is for outbound connections.
It might be that your ASUS is combining two things into one UI for convenience. Mapping one IPv6 prefix on the WAN to another on the LAN is one thing. Allowing traffic to a particular IP:port to cross from WAN to LAN is another. They're independent, though of course both are needed for the overall high-level task of "allow my LAN server to be reachable to the internet", so it makes sense to have a UI that does both things under the hood.
When you do a IPv4 "pinhole" port map you get precisely one mapping and it will timeout eventually, which can lead to all sorts of exciting debugging opportunities.
IPv4 does have 1:1 NAT but there are so few IPs so whilst I have a /24, 2 x /28 and 2 x /29 to play with and others, I doubt most do.
NPTv6 maps an entire address space from A->B and is actually not designed to deal with NATv4 anyway. It is for outbound connections.