With Server 2019, if you are not using a Windows Domain, you can get the error message
remote desktop licensing mode is not configured remote destkop services will stop working in 107 days. On the RD Connection Broker server, use Server Manager to specify the Remote Desktop…
This is difficult to track down, but basically turns out that you must configure localhost (the machine you're on) to be the license server. You can only do this in a per device licensing mode.
Following two are pretty decent explainations. The second (a Youtube Video with no sound) does a walk through.