I don't have much IPv6 experience, but some cursory Googling got me these points to check.
Do you have a IPv6 public address from your ISP, that would be a requirement.
You can add the parameter -Djava.net.preferIPv4Stack=false to the JVM_OPS and update the ip.address in the servers.properties file to blank, it may be 0.0.0.0. That should force the Minecraft server to prefer IPv6.
You'll also ned to enable IPv6 in your docker settings in Unraid - Reference