A black line on a mobile screen can indicate several issues. It might be caused by a hardware malfunction, such as a damaged display, a loose connection, or a defective graphics processor. Software problems, such as corrupted updates or apps, can also result in visual glitches. In some cases, restarting the device or contacting a technician for repair may resolve the issue. https://smartphonecrunch.com/black-line-on-mobile-screen/