I used to type ::1:9092 to connect to my Kafka brokers on my laptop. Best shortcut ever.

that would suggest your app isn't listening on the v6 address

so you are already testing it :)

I don't think so.

I get the same result when I run "ncat -6 -lp 80" inside the container and try to wget from the outside.

When I do the wget inside the container, I get "Connecting to [::1]:80... failed: Cannot assign requested address.".

As I said, reading around the net about "docker ipv6", it seems Docker is not IPv6 ready out of the box.

That is correct - please first enable ipv6 and assign it a subnet in your /etc/docker/daemon.json, then restart the service. Details at: https://docs.docker.com/config/daemon/ipv6/