Any web server such as IIS, Nginx, or Apache allow HTTP/2 to the turned on or off at the listener/port binding level.  So if a web server is listening on port 80 and 8080, HTTP/2 can be one for one of those and off for the other.

Undertow does not seem to allow this as discussed in this thread on the mailing list. 

https://groups.google.com/g/undertow-dev/c/6Ibj-PffiGE/m/NI_A5IM6BAAJ 

The option is ignored when passed as a socket option and can only be specified globally for the entire server.