It can be as simple as a worn or partially disconnected ribbon cable, but the middle section makes me believe that there is physical damage to the screen. Without practicality, it’s hard to say.
Your choices are … replace or replace the cable and see if it improves, or take it to a professional. The cables are very fragile, and this new Mac can be covered if it does not cover the terms.
Testing an external monitor eliminates any doubt about the GPU. An additional test would be to take a screenshot and view it on the external screen.