As problem is described in https://issues.redhat.com/browse/ODC-3458 we need to provide additional information on how to clean up knative custom resources that are not removed if Serverless is uninstalled.

Administrator must remove those CRDs to make the Serverless UI be removed from OCP.

To remove those CRDs invoke:

oc get crd -oname | grep -E '(serving|internal).knative.dev' | xargs oc delete

Those CRD should be removed after deleting the Knative Serving CR as point number 3 - here