Theirs horizontal black lines on my screen how do I get rid of them

Reset PRAM:  Reset NVRAM or PRAM on your Mac - Apple Support

Settings that can be stored in NVRAM include sound volume, display resolution, startup-disk selection, time zone, a            Click inside the box to choose an option.nd recent kernel panic information. The settings stored in NVRAM depend on your Mac and the devices that you're using with your Mac.

If this doesn't help, contact Apple.

Click inside the box to choose an option.

Support.  https://getsupport.apple.com/?caller=kbase&PGF=PGF63005&category_id=SC0245&symptom_id=23362

I also started getting horizontal lines 2 mm apart on my screen. Lines would vanish when screen was closed to a smaller angle (30 degrees) and then reappear, when opening wider. Also experienced occasions ghosting of images or overlapping app windows. Took the MBP 16 to the Apple Store for further diagnosis. Techs diagnosed that it is likely a loose display cable or a faulty display. They offered to check for a possible loose display cable and re-seat it. If not resolved, said display would have to be replaced. For what it’s worth. (Apple offline and online diagnostics performed all indicated no other hardware problems, with the GPU, etc. Problem seemed to be diagnosed. Attaching an external display is also helpful in diagnostic of the GPU.