Diagnosis
That's likely pressure damage or a minor defect in the IPS panel itself, often from something pressing on the screen in the bag or from the "smart cover" magnet being too strong in one spot. It's a physical panel issue.
How to Fix It
For very faint uniformity issues, sometimes cycling the power on/off a few times can help (unplug everything, wait a minute). But true pressure marks are permanent. Your only recourse is a warranty claim if it arrived like that or appeared under normal use.
If That Didn't Work
Rule out a video source problem. Connect the monitor to a different device (a phone, another laptop). If the lines/shadow are in the exact same spot, it's the monitor. If they change or disappear, the problem is with your original device's graphics output.
Heads Up
Be super careful with the smart cover. When you close it, make sure there's nothing like a keyboard key, pen, or headphone plug sandwiched between the cover and the screen. Even slight pressure in the bag can cause permanent marks on these thin panels.