Congrats @lstrobel, you have a K8s cluster now!
We have a few users facing the same problem with IPv6 and the registry [1][2]. What worked for most people is to edit /etc/hosts and comment out the ::1 localhost ip6-localhost ip6-loopback line (suggested in [1])
[1] https://github.com/ubuntu/microk8s/issues/196#issuecomment-443869365
[2] https://github.com/ubuntu/microk8s/issues/498