To enable dual-stack networking use the following k0s.yaml as an example. This settings will set up bundled calico cni, enable feature gates for the Kubernetes components and set up kubernetes-controller-manager.
spec: network: podCIDR: "10.244.0.0/16" serviceCIDR: "10.96.0.0/12" calico: mode: "bird" dualStack: enabled: true IPv6podCIDR: "fd00::/108" IPv6serviceCIDR: "fd01::/108"
Calico doesn't support tunneling for the IPv6, so "vxlan" and "ipip" backend wouldn't work. If you need to have cross-pod connectivity, you need to use "bird" as a backend mode. In any other mode the pods would be able to reach only pods on the same node.
k0s.yaml dualStack section will enable all the neccessary feature gates for the Kubernetes components but in case of using external CNI it must be set up with IPv6 support.