The example output mentioned in the docs is incorrect. https://docs.redhat.com/en/documentation/openshift_container_platform/4.18/html/security_and_compliance/cert-manager-operator-for-red-hat-openshift#cert-manager-istio-creating-issuer_cert-manager-operator-integrating-istio

Update the doc sample with this code: 
apiVersion: cert-manager.io/v1
kind: Issuer
metadata:
  name: selfsigned
  namespace: <istio_project_name>
spec:
  selfSigned: {}
---
apiVersion: cert-manager.io/v1
kind: Certificate
metadata:
  name: istio-ca
  namespace: <istio_project_name>
spec:
  isCA: true
  duration: 87600h # 10 years
  secretName: istio-ca
  commonName: istio-ca
  privateKey:
    algorithm: ECDSA
    size: 256
  subject:
    organizations:
      - cluster.local
      - cert-manager
  issuerRef:
    name: selfsigned
    kind: Issuer
    group: cert-manager.io
---
apiVersion: cert-manager.io/v1
kind: Issuer
metadata:
  name: istio-ca
  namespace: <istio_project_name>
spec:
  ca:
    secretName: istio-ca

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