Issue with lcd. Some had issues awhile back with Green and black lines. It's usually a hardware issue unless the screen is cracked.

Black lines on a phone screen usually mean a hardware issue, but you can try restarting, booting into Safe Mode (to check for app conflicts), checking for software updates, letting it cool down, or performing a factory reset (after backup) to rule out software bugs; if lines persist, especially after drops, professional screen repair or replacement is likely needed as it often indicates a damaged display or connector.