This solution fixes two issues:

- a black Screen appears in Remote Desktop under Windows 10 Pro v.1903 

- the mouse vanishes (not usable) on the second screen when using a dual screen setup

The issue is related to XDDM vs WDDM display driver models. 

You will need to change a GPO to force use back the old XDDM display driver. 


- go to Computer Configuration > Policies >Windows Settings >Administrative Templates >Windows Components >Remote Desktop Services >Remote Desktop Session Host >Remote Session Environment], 

- set the Policy [Use WDDM graphics display driver for Remote Desktop Connections] to Disabled.

Microsoft employee Denis Gundarev confirmed that it was a known issue:

Display drivers report some of their capabilities upon load. In previous Windows versions this reported data wasn’t used or verified. 

Because of that, some of the old versions of the legacy display driver may report invalid data and it would be ignored. Starting with Windows 10 1903 RDP uses this data to initialize the session.