Hello,
I am currently trying to host a 1.20.1 Forge server (via IPv6), but I always get the error ‘the address family is not supported by the protocol family’ when trying to connect to the server via IPv6 (+Port). However, if you then connect to the server via IPv6 using normal Minecraft (1.20.1), it works.
And if I host a normal Minecraft server on 1.20.1, there are no problems at all.