Istio and HTTP2

Please help me to make some order in the information about moving Istio Mesh (on Kubernetes) to communicate (both internally and externally) using HTTP2.

Source #1: This post suggests to update Mesh configuration for h2UpgradePolicy: UPGRADE

Source #2: Istio documentation talking about explicitly setting Service protocol (http2 is one of supported protocols).

I’m a bit confused: are these ways (#1 and #2) somehow related? Or these are two different approaches to achieve the same?