about_Sue wrote:
After the December update, my MacBook Pro, a 2019 16-inch model, only shows a black screen when I disconnected it from the monitor to use portably.
Even when I increase the brightness, the screen remains black. However, when I come home and connect it via HDMI, the screen appears. It shows the screen only during boot, and later turns black.
I've tried resetting the MacBook to factory settings and all possible methods, but the screen still displays only when connected via HDMI. Is there a solution?
An external monitor activates the Discreet GPU the default is the Integrated GPU.
A GPU demanding app— for example the Photos.app will also trigger the Discreet GPU independent of an external monitor— this would be a good test in trying to determine the issue.
On the Intel Mac you can try
Try resetting NVRAM/PRAM Reset NVRAM on your Mac - Apple Support
hold the keys down for several rounds of reset.
If no change there is no harm in resetting the SMC Reset the SMC of your Mac - Apple Support
and compare your results.
Can you run the "user" Diagnostic...not as definitive as Apple's own AST2 (Apple Service Toolkit) back bench diagnostic, but may kick out an error code or it may not.
Use Apple Diagnostics to test your Mac
Use Apple Diagnostics to test your Mac - Apple Support
In or out of warranty you can get a free "Apple Service Diagnostics" test /assessment this is a back bench test— not the user facing "Mac Resource Inspector" (MRI) they show you initially.
Make an appointment for a "hardware issue"
Genius Bar Reservation and Apple Support Options - Apple
Outside the USA
Contact Apple for support and service - Apple Support
