DIAGNOSIS This is a panel or T-Con (Timing Control) board fault. A vertical line present on all content indicates a hardware failure in the display driver or connections.
FIX Perform a panel self-test to isolate the issue. With the TV off, press and hold the VOLUME DOWN button on the TV itself (not remote). While holding it, press the POWER button on the remote once. The TV will start and display a solid color screen. If the line is still present, the panel is faulty.
IF THAT DIDN'T WORK If the line disappeared during the self-test, the issue is with the main board output. Try a factory reset (Settings > General > Reset to Initial Settings) to clear any corrupted video processing firmware.
HEADS UP Do not attempt to physically press on the screen. This is not a temporary stuck pixel issue. Document the line with photos/video for LG warranty service. The 65NANO75UQA panel has a specific warranty period separate from the main unit.