Again, to me the OP is talking explicitly about places where you have to enter it in. What are the other mechanisms? Let’s forget about situations where you can copy/paste or use DHCP.

My answer would be to use my phone to take a photo of the address (if not easily accessible via web browser), and then use that to manually enter it. Probably not a situation where you can rely on memory, unfortunately.

Outside of the NIC and DNS, where else do you need to enter in an IP literal?

Firewalls, for example. We have huge files containing risk levels for various IP addresses. Most of it is automated, but sometimes we have to tweak something manually. These aren't IP addresses that we control, so DNS isn't helpful. Often we're dealing with ranges as well, for which DNS is also unhelpful.

Technically, you could claim you're authoritative, just hope the assignments don't leak ;-)

Connecting to things on your local network

Dns resolver Internal IPs

So you gotta log into your registrar and copy paste your IPv6 address and wait god knows how long for it to propagate...

DNS doesn't actually "propagate", all you're waiting for is the caches to expire, and you can control that by keeping a low TTL on the record.

Or you can host your own dns. Or you can get a decent dns host. It doesn’t need to be your domain registrar, much like you don’t need your website or email hosted with your domain registrar.