MacBook Pro 16" (2019 model) cannot be used with internal and external display because the computer overheats, and throttles. 

The problem is described in detail in this youtube video:
https://www.youtube.com/watch?v=6mS4AAdft_M

Description of the problem:
Using an external display with the Macbook Pro 16" causes the macbook to become really hot (69 to 75 degrees).
The reason for this is that when you use an external display as well as the laptop display, the power drawn by the DGPU (Dedicated GPU) jumps from 4w to 17w.

• Use the laptop display alone (using the DGPU), it only draws around 4w.
• If you run a 1080p external display in clamshell mode, again the DGPU only draws 4w
• If you run 2 x 1080p external monitors in clamshell mode, the DGPU draws 5w
• If you run the internal display opened with an external display the DGPU draws 19w

The temperatures can get so high that the integrated fans are unable to cool down properly the machine even running at maximum speed. Sadly this causes very high overall temperatures, and throttling of CPU/GPU, rendering the computer unusable.

Example:
Using the computer with external display in a summer day with 27-28º is impossible because of imminent throttling caused by the high temperature of the DGPU.

We ask for
Apple, please acknowledge that this isn't "expected behaviour" and find a solution, to fix our very expensive computers.