AdiIRC

Would I still be able to join froma ipv6 IP?

IPv6 does not appear to be working in AdiIRC 3.1.
DNS is correctly resolved but then fails with "Unable to connect to server: example.com", waits 5 seconds, and then successfully retries and connects to the IPv4 alternative.

Do you have a working IPv6 connection https://test-ipv6.com ?

Have you checked other clients such as mIRC using the command /server -6 chat.freenode.net or hexchat?

Also if you are using any type of firewall, make sure AdiIRC is allowed to make ipv6 connections through it.

AdiIRC is completely allowed in all 3rd party firewalls and Windows Firewall is set to allow all incoming and outgoing connections. It's also the only program I run that has trouble connecting to IPv6 hosts.

So mIRC and/or hexchat works with IPv6 connections? e.g the port 6667 is not blocked from your isp?

What network are you trying to connect to?

Is it a TLS/SSL or plain connection?

I am on freenode right now through IPv6.

Ah, this is somewhat embarrassing, ZNC is listening on 0.0.0.0 instead of ::.
I should have checked that first, my bad.

No worries, glad you got it figured out :)