Short answer: cracks, lines, flickering, dark areas, backlight problems and an image that changes when the lid moves all deserve professional evaluation.
Five warning signs
- Visible cracks or damaged glass
- Vertical or horizontal lines
- Flickering or intermittent images
- Dark areas or uneven backlighting
- A display that changes as the lid moves
It may not always be the screen
Cables, hinges, backlighting and other components can create similar symptoms. Diagnosis helps avoid replacing the wrong part.
Protect your data
Back up important files whenever the MacBook remains usable. Bring the charger when power or startup behavior is part of the problem.