We can document disableRoute for DomainMapping (not documented but already tested) to customize TLS for the custom domain.

With said, there are many ways to support custom TLS for custom domain recently as:

ALREADY EXIST
a) Use net-kourier and ServiceMesh (documented)
b) Use disableRoute for DomainMapping (This Jira ticket)

NEW
c) Use net-istio and ServiceMesh (documented & tech preview v1.16+)
d) Use spec.secretName in DomainMapping (not implemented in downstream but would be possible to support with https://github.com/knative/serving/pull/11250)

Using disableRoute is an escape hatch. We should consider if we sill expand the escape hatch documentation or not.

(This was a little bit discussed in another docs PR https://github.com/openshift/openshift-docs/pull/33179 so link here.)