Diagnosis
This is a column of dead or stuck pixels, or a failure of the LCD panel's gate driver circuit. It is a hardware fault.
How to Fix It
First, perform a basic pixel refresh. One: Power off the monitor for at least one hour. Two: Run a pixel exerciser video (e.g., a rapid color cycling video on YouTube) at full screen for 30-60 minutes. Three: Gently massage the area of the line with a clean microfiber cloth while the monitor is off, applying very light, even pressure. Do not press on the screen directly with fingernails or hard objects.
If That Didn't Work
The line is likely permanent. Check Samsung's dead pixel policy for your region. For the S36GD, policies often require a minimum number of dead pixels (e.g., 3 or more bright sub-pixels in a cluster) for a warranty replacement. A single vertical line may or may not meet the threshold.
Heads Up
Do not attempt to repair the panel yourself. There are no user-serviceable parts. A vertical line is almost never a cable or source issue. To confirm, disconnect all inputs. If the line remains on a solid-color test screen (accessible via the OSD Information menu), the panel is faulty.