Image Registry operator is in degraded state with error "Unable to apply resources: storage backend not configured"

Issue

• Image Registry operator is in degraded state with error Unable to apply resources: storage backend not configured

$ oc describe co image-registry

Name:         image-registry
Namespace:
Labels:       <none>
Annotations:  <none>
API Version:  config.openshift.io/v1
Kind:         ClusterOperator
Metadata:
  Creation Timestamp:  2020-08-21T07:38:14Z
  Generation:          1
  Resource Version:    13941691
  Self Link:           /apis/config.openshift.io/v1/clusteroperators/image-registry
  UID:                 fe1f6366-3834-4c47-b37f-67cd53b52c7c
Spec:
Status:
  Conditions:
    Last Transition Time:  2020-09-01T11:29:45Z
    Message:               Unable to apply resources: storage backend not configured