Unfortunately, it’s still not supported by Postman as of April 2019. Previous version of Postman used to be a browser extension and it wasn’t possible to fine tune the request. Newer versions, however, run as standalone applications which could allow more low-level control of the request.
See the following comment quoted from the issue #6242 which was opened early April 2019 requesting an option to specify HTTP protocol version:
You’ll be pleased to know that work is in progress for more low-level control over the request. Stay tuned.
As of June 2023, however, Postman haven’t shared any updates on this.
Depending on what you need, you could use curl. It provides a set of options that allows you to control the version of the HTTP protocol:
--http0.9: Tells curl to be fine with HTTP version 0.9 response.
--http1.0: Tells curl to use HTTP version 1.0.
--http1.1: Tells curl to use HTTP version 1.1.
--http2-prior-knowledge: Tells curl to issue its non-TLS HTTP requests using HTTP/2 without HTTP/1.1 Upgrade. It requires prior knowledge that the server supports HTTP/2 straight away.
--http2: Tells curl to use HTTP version 2.