According to the following KCS, it seems that Red Hat currently doesn't support Envoy Filter configuration in Service Mesh.

Envoy Filter in Openshift Service Mesh
https://access.redhat.com/solutions/5672521

However, according to the following document, it looks like that the Envoy Filter configuration is supported.

Configuring for case normalization
https://docs.openshift.com/container-platform/4.9/service_mesh/v2x/servicemesh-release-notes.html#configuring-for-case-normalization

It is necessary to make it clear that whether EnvoyFilter is supported or not. If it is not supported, it may be better to add a warning message to the above document. If it is supported, the above KCS needs to be modified and/or made Retired.

Also, if EnvoyFilter is not currently supported, the customer hopes to know the schedule about when or which version it will become supported if there is any fixed schedule.