I assumed display damage because every time I’ve seen these artifacts it’s been due to a damaged display matrix, but i agree that if it’s intermittent and isn’t some kind of unusual defect in the display, the ribbon coming partially loose sounds most likely, followed by cable damage (e.g., pinched by lid hinge).

Ribbons are usually pretty secure, especially from factory if tape hasn’t been removed before, but with enough heat (e.g. left in car outside) and jostling, the tape can loosen, and cable’s weight plus jostling can be enough for ribbon to pull itself out.

To quickly check without opening case i would try lifting the machine in two hands and driving it gently but firmly into your right palm (which would jostle the ribbon toward/into its terminal). If it’s loose, i would expect to see the display respond in some way after at most a few tries, if the ribbon cable is loose. If not, it’s still worth opening and re-seating ribbon to be sure, but jostling it a bit should immediately worsen or improve the visual artifacts, confirming the diagnosis.