Macbook shutting down after a screen glitch

My 13" MacBook Pro (Late 2017) with MacOS 11.4 started to behave weirdly today:

After a few seconds, it goes black, just like it was turned off – but it is not. I have to turn it off by long-pressing the power button, and then I can bring him back to life.

I was having another screen plugged in the first time it happened and the glitch appeared first on the screen, and then after ~5 seconds on my MacBook' screen.

What might be the reason for such behavior?

Solution 1:

Honestly the first thing I would have advised is to plug in an external monitor. Whoops you already have done that.

So if that happens on both internal and external displays it is not the display itself. Instead I would tend to blame the GPU (graphics hardware subsystem). Especially as the system doesn't shut down, rather it has to be manually shut down.

That said it might be worth your while to back up your system, wipe the drive and reinstall macOS. If the problem does not return well I was wrong and it was something in macOS causing this.

But honestly too many years doing computer support for a living it smells like a hardware issue. So it may require repairs at your local Apple repair shop.