https://www.envoyproxy.io/docs/envoy/latest/start/quick-start/run-envoy says that starting envoy with the given demo config envoy-demo.yaml should result in:

The Envoy admin endpoint should also be available at http://localhost:9901

It doesn't seem to working, as the admin section is not enabled in the config.