A patch which implements this functionality was sent upstream and applied to downstream:

https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg04800.html

build:
http://brew-task-repos.usersys.redhat.com/repos/scratch/sjubran/mingw-qemu-ga-win/7.6.2/3.el7ev/

Test with this build, can get correct win2019 guest os info.
result:

{"execute": "guest-get-osinfo"}
{"return": {"name": "Microsoft Windows", "kernel-release": "17763", "version": "Microsoft Windows Server 2019", "variant": "server", "pretty-name": "Windows Server 2019 Datacenter", "version-id": "2019", "variant-id": "server", "kernel-version": "10.0", "machine": "x86_64", "id": "mswindows"}}

Hi Amnon, Sammeh,

The provided package(mingw-qemu-ga-win-7.6.2-3.el7ev) is for rhel7, should we generate one for rhel8?

Only one version is better from packaging point of view.

Hi Amnon, Yan,

What's the plan about version issue?

Test with mingw-qemu-ga-win-100.0.0.0-3.el7ev, can get correct win2019 guest os info.
result:

{"execute":"guest-get-osinfo"}
{"return": {"name": "Microsoft Windows", "kernel-release": "17763", "version": "Microsoft Windows Server 2019", "variant": "server", "pretty-name": "Windows Server 2019 Datacenter", "version-id": "2019", "variant-id": "server", "kernel-version": "10.0", "machine": "x86_64", "id": "mswindows"}}

Change the bug status to verified.