In practice HTTP/2 forces encryption. For example Amazons ALB docs say "Considerations for the HTTP/2 protocol version: The only supported listener protocol is HTTPS." [1]

[1]: https://docs.aws.amazon.com/elasticloadbalancing/latest/appl...

My Apache server is fine speaking HTTP/2 over port 80:

  curl -v --http2 --http2-prior-knowledge http://localhost
  * Connected to localhost (::1) port 80 (#0)
  * Using HTTP2, server supports multi-use
  * Connection state changed (HTTP/2 confirmed)
  * Copying HTTP/2 data in stream buffer to connection buffer after upgrade: len=0
  * Using Stream ID: 1 (easy handle 0x559a7c6545c0)
  > GET / HTTP/2
  > Host: localhost
  > user-agent: curl/7.74.0
  > accept: */*
  > 
  * Connection state changed (MAX_CONCURRENT_STREAMS == 100)!
  < HTTP/2 301 
  < date: Fri, 06 Aug 2021 11:16:05 GMT
  *snip*

Sadly none of the services that I reverse proxy through Apache support HTTP/2..

It make sense that internet facing clients and servers only support HTTP/2 over TLS. But that is different for internal connections or debug tools.