As of Kernel 773 there is the parameter icm/HTTP/client/support_http2 (default value FALSE, as of Kernel 777: default value TRUE). But not sure when exactly http/2 is used. The http destination's options in SM59 allow only to choose between HTTP 1.0 and 1.1.
https://www.rfc-editor.org/rfc/authors/rfc9113.html
https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md
https://bkubiak.github.io/grpc-raw-requests/