Broadcom has listed Windows 2019 in our platform matrix (PSM) as a supported OS platform for the overall product stack (Provisioning and Connector servers etc.,). At the time of publication, we did not scrutinize the Redhat OS support matrix, however as you have correctly noted, it does not show Windows 2019.
We reached out to the Redhat team to discuss another customer issue and they mentioned, the platforms listed in their documentation are tested configurations but that doesn't mean that it will not work. Although it is not listed in Redhat's platform matrix, as part of our pre-release schedule we checked and tested it on Windows 2019. So far no errors have been identified or reported.