Metric Data is not displayed

I’ve got some general Problem regarding Metrics in Opensearch. I run Opensearch and Opensearch-Dashboards from the Helm Chart inside a Kubernetes Cluster. There I want to monitor the Metrics from one or more Kubernetes Clusters.
I tried it with different Aproaches which are all ending the same: I got a metric Index with thousands of Dosuments and a mapping that looks like they belong to metrics, but when I got to the Metrics Tab (Observability>Metrics) there is absolutly nothing to see.
Does anybody can help me with what is the Problem here.
At the Moment I think there is some thinking Error on my Side…