MacBook Pro 2011: vibrating horizontal dotted lines all over the screen

I have had the well known AMD GPU failure on my 2011 MacBook Pro. Thanks to the instructions of Nimesh Neema, I have successfully disabled the AMD GPU and enabled the onboard Intel GPU. Fantastic!

Next I rebooted my MBP about 6 times, and all was working and normal. When I unplugged the power cable to move the MBP to another location, the screen went black. Touching any keyboard button or the power button, did not reactivate the screen. So I pushed the power button for 4 sec's, waited a bit and then powered the MBP up again.

Unfortunately, immediately after booting when the screen turns on, it showed vibrating horizontal dotted lines all over the screen, as in the attached picture (not the well known grey/pink vertical lines). The booting works normal, logging in works, all applications work. But the screen is terrible with these lines.

Does anyone recognize this?

Is this a malfunction of the Intel GPU?

What can I do?

Does it do this on an external screen? This would show the difference between the GPU being bad or the display going bad. Being you had to hard shut off the laptop I am leaning to GPU being bad.