The dropdown of available metrics on the query browser page shows a generic message when it fails to fetch the metrics from the Prometheus API. A common reason for the API call failing is that the user does not have access to the API. In this case, it would be more helpful to show a message saying that.
Created attachment 1714359 [details] error info before the fix
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory (OpenShift Container Platform 4.6 GA Images), and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. https://access.redhat.com/errata/RHBA-2020:4196