Ideally using ipv6 without NAT, but yeah hole punching or quic address discovery like iroh does works too

and how do you discover the ipv6 address? memorize it? many ISPs don't listen to informational documents listing all the problems with random dynamic prefixes.

You can use either iroh directly or do it like them with dns via pkarr and use mainline DHT and ed25519 public keys that you can share via separate channels

https://app.pkarr.org/

https://www.iroh.computer/blog/v1

Dynamic DNS is fine for many use-cases.

I suppose, but then everybody else knows your IP too, which nullifies one of the benefits of IPv6.

by using something like iroh.

basically an embedded tailscale.