Some NAT46 (not to be confused with NAT64) tools and routers exist in the wild today. "Stateless" ones work by manually setting routes for chosen IPv4 addresses to IPv6 ones or treating all of IPv4 traffic as the "ultimate" semi-private IPv6 "subnet" and prepend a fixed IPv6 prefix to all IPv4 traffic (and you can do that with just about any IPv6 /64). Stateful ones act a lot like NAT44 routers and can also use "out-of-bound" protocols similar to NAT44's UPnP (but I think distinct from?) to setup routes on the fly from application requests.
Though they exist, my understanding is that the need and use cases for them is overall much weaker than NAT64 or NAT44.
If the internet destinations I want to reach have an IPv4 address, it's obviously very easy. It's just a kind of NAT. And everywhere I want to reach has IPv4 addresses and probably will for a long time.
If they're IPv6 and I really need to reach them anyway, then I could imagine writing a special NAT that keeps a database equating IPv4 addresses (that I make up) with real IPv6 addresses on the net and doing a NAT that way. That would be suboptimal because it would mean that I'd need to add a database entry in advance for each internet destination, of course. But it seems feasible. And I can think of a couple of ways to automate it.
But, honestly, I don't know. I'm just spitballing what the best way of handling all of this actually is. Every method I have heard or can think of has some serious downside, and I don't have sufficient expertise (and haven't spent the time) to do actual cost/benefit analyses of the various options yet.
This is all a huge time-consuming hassle, and is why I'm putting the whole thing off until I have no other option.
Though they exist, my understanding is that the need and use cases for them is overall much weaker than NAT64 or NAT44.