MBP 2017 w/ Touch Bar: How to turn off internal display & use external display instead Configuration:  I have a MacBook Pro 2017 with Touch Bar connected to a 27" external display and a very fast external HD connected via Thunderbolt-3.

Problem:  I am unable to drive 4K or HD video in this configuration without constantly dropping frames (in Davinci Resolve.)  When I disconnect the external display and use only my laptop's display, the video plays significantly better -- almost perfect.  

Hypothesis:  I suspect the original configuration is a heavy lift for my laptop's graphics chip.  And the video may play fine if it is driving only one monitor instead of two.  

Goal:  I want to use my external display and not my laptop's internal display -- all the while keeping my keyboard and mouse functional.  (No, I do not want to turn the brightness down to 0 nor do I want to do mirroring.)

How do I do this?

Thanks in advance.
I have tried this as well with no luck for several months, then connected to docks and still stuck with internal display to be on.

Then I tried the hedge dock and similar and works well but using an external Apple Key and Mouse was my only solution.

I do know the Windows PC have that certain function and only seen it on older macs with Function keys nothing yet on MBP2016 and later w/TB

I would figure there must be a way via a terminal command.