Hi Luke,
As of yet, the PowerBuilder runtime is not officially supported on Windows Server 2019.
This does not necessarily mean that the PowerBuilder runtime will not function in Windows Server 2019, only that Appeon cannot yet certify its functionality or provide support for this environment.
You can consult the operating systems supported by Appeon PowerBuilder here:
https://www.appeon.com/support/documents/appeon_online_help/pb2019/installation_guide_for_pb/ch03s02.html
Support for runtime on this version of Windows Server should be added on a future release, however, it has not been specified on Appeon's roadmap yet.