Display screen went black off

You should get it diagnosed by visiting an Apple Store or Authorised Apple Service Provider next to your place.

Apple - Find Locations

Mac Repair and Service - Apple Support

From what I have read, the cable, which connects the display to the motherboard, is in most cases defective.

Does the display come back, if you slowly move it towards the keyboard?

<< the display suddenly went completely blank. ...

...an external display, it works perfectly fine.>>

<< This makes me believe the issue might be with the built-in display, or ... >>

Based on your debugging, your internal display appears to have failed.

<< ...the main display remains black.>>

that adds weight to the theory that the main display has failed.

Repair by replacement of a 14-in display at an Apple-owned store in the US is about US$500, a 16-in display is about US$800. (Caution: those prices are from memory.)

Your appointment of evaluation at an Apple-owned store if free, in warranty or out, and the quote to repair is Firm, no surprises. IF they can fix you problem in.a modest amount of time, without using spare parts, the repair is generally free as well.

I agree with Grant Bennet-Alder.

If you can, visit an Apple Store and get an estimate.

Looking at the price for a refurbished MacBook Pro M2, repairing would be an option.

Refurbished MacBook Pro M2 2023 - Apple Store-Refurbished

in the US, Consumer Reports magazine generally suggests that if the cost to repair an appliance (such as a clothes washing machine) exceeds Half the cost of a new one, you should get a new one.

They are generally discussing appliances that do not change nearly so quickly as computers.

But that gives you a place to anchor your thinking on the Repair/Replace issue.