In order to display cluster metrics, Lens requires that Prometheus is running in the cluster. You can install Prometheus in Cluster settings if needed.
Lens tries to detect Prometheus installation automatically. If it fails to detect the installation properly, you can configure Prometheus service address in Cluster settings. If some of the metrics are not displayed correctly, you can see queries that Lens is using here and adapt your prometheus configuration to support those queries. Please refer Prometheus documentation or your Prometheus installer documentation how to do this.