Screen Brightness accidently set to dimmest (blank screen) Android-x86_64-8.1-r1
This method requires adb:

With your device plugged in, issue a screen brightness change request:

adb shell settings put system screen_brightness 255


The number at the end of that command is a number from 0-255, where 0 is dimmest and 255 is brightest.

Note: if the above command doesn't work, you might have to issue this commend first:

adb shell settings put system screen_brightness_mode 0