Hi @larslevie, thanks for your question.
The log about admission webhook is not related - we do a best effort validation of the Pod spec using dry-run API if it's available. If not, we log the log you see but we don't stop the reconciliation.
I tried the spec you pasted, it does work for me, so to debug further, could you take a look at the StatefulSet that ECK is creating for this ES? You can do that by running kubectl describe statefulsets.apps quickstart-es-default. If it exists (it should), events can tell you more about why Pods are not being created.