Fake broken pixel on Windows 10

A couple of months ago I discovered that I have broken pixel on my laptop screen:

The weirdness of it is that it isn't a broken pixel at all, because as you can see I'm able to screenshot it.

The first time it appeared, I just rebooted my laptop a couple of times and it was gone, but this time it won't leave me even after 10 reboots and "screen fixer" for stuck pixels.

I can hover the mouse over it, and I can record it on video, but when I open exclusive fullscreen applications like games (CS:GO in my exact case), it doesn't show up.

I did a virus scan and I don't have any pirated software installed. No new software/updates were installed recently.

Important note: it appeared in the same place as the previous time, but when I change the resolution of the screen it does move a bit.

That's not even a fake broken pixel. It's a 1×1px window – it even has the same Windows 10-style shadow that windows usually have.

It might be a window that is supposed to remain hidden (programs often use invisible windows because that's required for receiving e.g. global keyboard shortcuts or other system events), yet sometimes – due to bugs in the software – such windows end up being listed in Alt+Tab or even shown on-screen anyway.

Various "Task Manager replacement" tools (such as Process Explorer) have a function where you can just point at a window and the corresponding process will be highlighted. This will narrow it down to a specific program.

The regular Windows 10 Task Manager also has a "Startup" tab where all the startup programs can be disabled. Try disabling them all; if the pixel disappears, re-enable one, or half of them¹, repeating until you find the one that's showing the window. (Although there is a small chance that it's launched by a service and not by a startup program.)

^{¹ (Systems tend to accumulate so much cruft in the "Startup" list that I suspect you should just keep the remaining half permanently disabled anyway...)}

Go into safe mode, and start running everything that you usually run. An application is causing this issue, so when you start an application and you see the pixel again, you know that that application is causing the issue.

You mentioned CS:GO, so I assume you're running Steam.

Steam has some very poor window management methods. I personally deal with it leaving a title-bar-sized chunk of screen real estate allocated as its window even when minimized, even though it never actually paints those pixels, causing strange artifacts in the windows stacked below it.

Open task manager and kill everything associated with Steam and I suspect your black dot will disappear.

I have had this issue arise on one of two identical 144hz monitors; ironically, it turned out to be the newer one. Of course, a component being older than another doesn't mean it will fail first; but in my mind it was still strange.

As above, I would check for any open applications that might be "squeezed down" to fit the aforementioned 1px/1px box. After closer inspection, I found that it wasn't a fault of the monitor (thankfully, in this current climate); but rather a window whose non-maximised size was squeezed into the aforementioned 1 pixel box.

My reasoning for why it looks that way is that the standard white toolbar across the top of the window is "sandwiching" the application... but since a variety of colours or shades cannot be represented by one pixel, it shows black (and trying to represent it would probably crash Windows).

In short, reboot and you'll be golden. As for why this happens... I'm as lost as you.