Following doc to enable user monitoring and after creating an application project and application that has its own metrics as developer user.
After going in developer console > Observe > metrics > Select an Query > custom query > Here query will not auto complete for application metrics unless below permission are added

kind: ClusterRole
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: metrics-autocomplete
rules:
  - verbs:
      - get
    apiGroups:
      - monitoring.coreos.com
    resources:
      - prometheuses/api
    resourceNames:
      - k8s

This role should be there by default and should be mentioned in the steps for user monitoring.