There's a vertical line that just appeared on my screen (14' M3Pro)

Full Height Vertical artifacts (goes through the Menubar as well as the opened widows) are almost always failures in the display assembly itself.

The litmus test is to examine a screenshot.

If the defect is NOT present in the screenshot, the issue IS almost always the display assembly.

you can work-around by connecting an external display.

Either view the resulting screenshot on another device, or make sure to move the picture to the side so that the screenshot does not line up with the screen so you can see if the defect exists ..... you cannot tell if the screenshot lines up with the display.