As asked in http://post-office.corp.redhat.com/archives/serverless-interest/2020-August/msg00001.htm it is better to add more explanation about gRPC supports.

The fix needs OCP 4.5 or later doc.

Copy the Mail discussion below from the above mail.

Q. Quick question - gRPC support for OpenShift servless indicates that it is not supported through routes as the HAProxy does not support HTTP/2 (which is not correct). Is this only a doc issue or is it something else?
 
https://docs.openshift.com/container-platform/4.5/serverless/serving-creating-managing-apps.html#interacting-serverless-apps-http2-gRPC_serving-creating-managing-apps
 
A.  It is true that gRPC request through route (external access) is not supported on OpenShift Serverless unfortunately.

OpenShift Route supports HTTP2 since 4.5 but it does not support insecure or edge-terminated routes as explained in [1].
Unfortunately OpenShift Serverless supports only insecure or edge-terminated routes. That is why, it still cannot support HTTP2/gRPC.
(Sorry we created the doc around 4.2 or 4.3 so it does not explain it enough about this. I will update it.)

[1] https://docs.openshift.com/container-platform/4.5/release_notes/ocp-4-5-release-notes.html#ocp-4-5-http-2-ingress-support
> "The connection from HAProxy to the application Pod can use HTTP/2 only for re-encrypt routes and not for edge-terminated or insecure routes."