macbook air screen goes dark when i open the lid all the way

Is it the backlight or the whole picture going? At the angle where it goes dark, shine a phone torch at the screen. If you can see a faint picture, just the backlight is going. Plug into an external monitor too. If that's fine at any lid angle, it's definitely the display side and not the Mac itself. Get a quote for just the cable before agreeing to a whole display.

Display cable in the hinge, almost certainly. It wears from the lid flexing and cuts out past a certain angle. No software fix, it's a repair job.