IIS SERVER_PROTOCOL never returns HTTP2 (HTTP/2)

Using Windows Server 2025, I can not get the "SERVER_PROTOCOL" response header to return anything other than HTTP/1.1:

For example, a simple classic ASP page with:
<% Response.Write(Request.ServerVariables("SERVER_PROTOCOL")) %>

Always returns "HTTP/1.1".

I have verified the page is served via HTTP2 via developer tools in the browser and it's even upgraded to HTTP3/QUIC later on in the response sucessfully.