I cannot find any information about support HTTP/2 features in Typhoeus gem. Is this fully compatible or not?
Yes, it's supported, according to https://github.com/typhoeus/typhoeus/issues/628#issuecomment-496976697 you can create an HTTP2 request with:
response = Typhoeus.get("https://nghttp2.org", http_version: :httpv2_0, verbose: true)
and you can check the HTTP version with:
response.http_version
=> "2"
Remember that Typhoeus use libcurl and it has support for HTTP/2, but the underlying cUrl version needs to have support compiled in, so you use an old version, your results may vary.