Through Kube-OVN does support both protocol subnets coexist in a cluster, Kubernetes control plan now only support one protocol. So you will lost some ability like probe and service discovery if you use a protocol other than the kubernetes control plan. We recommend you use only one same ip protocol that same with kubernetes control plan.
To enable IPv6 support you need to modify the installation yaml to specify the default subnet and node subnet cidrBlock and gateway with a ipv6 format. You can apply this v6 version yaml at installation step 3 for a quick start.