If you could attach an external display, to see if the signal there also goes 'black' too;
that would indicate what part(s) may be defective in the MacBook. ~ In some, when
display is closed and the signal to it appears lost, there are electronic parts in both
the upper case and in the display. These can be failing to indicate position of panel.
Troubleshooting may be more involved than the simplistic overview suggested. In
that the internal display/lid may need to be closed to view an external. That can be
useful if effects are noted, and the repair shop is aware of any odd happenings.
A visit to 'authorized Apple service' should be considered. Some offer "mail-in" service.
• Apple Repair and Repair Status Check - Official Apple Support
https://support.apple.com/repair
• Get Support - Apple
https://getsupport.apple.com/
Good luck & happy trails!🌻🌤