It does exist though. The OS part is 464xlat and the router part is NAT64. You can try the second part out by setting your DNS server to one of the ones listed on https://nat64.net/, which will work with hostnames. To get IP literals to work you need 464xlat, which is currently a bit annoying to set up on Linux.

(Note that using the servers provided by nat64.net is equivalent to using an open proxy, so you probably don't want it for general-purpose use. You would probably want either your ISP to run the NAT64 (equivalent to CGNAT), or to run it on your own router (equivalent to NAT).)

The standard prefix for NAT64 is 64:ff9b::/96, although you can pick any unused prefix for it. ::ffff:0:0/96 is the prefix for a completely different compatibility mechanism that's specifically just for allowing an application to talk to the kernel's v4 stack over AF_INET6 sockets (as you figured out). It was a confusing choice of prefix to use to describe NAT64.