One of the main features of HTTP/2.0 is Server Push. Whenever it is available—by which I mean it gets the support of the protocol from the server and client browser—it lets the server send ("push") data to the client before the client asks for it.
This is one of the most popular features in JSF 2.3 and probably the one that demands less effort to use if your application is based on JSF—just migrate to a Jakarta EE 8-compatible server and then you are done.
This recipe will show you how to use it in your application and will even let you compare performance between HTTP/1.0 and HTTP/2.0 in the same scenario.