cert-manager is a Platform Agnostic Operator per https://access.redhat.com/support/policy/updates/openshift_operators.

As a Platform Agnostic Operator, there will always be a version of the operator available for every supported version of OpenShift at any given point in time.

cert-manager 1.13 was released and does not have support for OCP 4.12. 4.12 is still live and so any customers on OCP 4.12 using cert-manager does not have a compatible cert-manager if they want to get a fix, etc.

Docs and https://access.redhat.com/support/policy/updates/openshift_operators page will need to also reflect the updated compatible versions of OpenShift.