Question How can I tell if my graphics card or my monitor is the problem?

Sep 13, 2019
Here's my setup: Surface Book 2 13.5" with a USB-C to DP adapter connected to a Samsung CF791 34" 3440x1440 monitor.

Before I ever got this monitor, my laptop has had some strange little visual glitches in the form of pixel-y black lines appearing on the screen very briefly - for about one frame, maybe. Then, I got the monitor, and it struggles to stay on (especially if a game or full-screen video is playing), as you can see in this GIF. The black lines also appear on the monitor. I took these pictures while I was just moving my cursor in circles. The lines are also appearing as I type this out. Ctrl + Shift + Win + B, or restarting the video drivers, fixes the black screen problem (until it happens again).

My main question is: can I be sure that this is an issue with my laptop and not the monitor? I really don't want to repack the monitor and lug it to the nearest post office.

As for the laptop, it's out of warranty, so there's not really any option for me to send it in unless I pay $600 for a replacement. I've already restarted it, done a near factory-reset (only keeping my personal files), and uninstalled and reinstalled drivers. Temperatures are completely normal when these issues happen, and while I'm gaming, the GPU is around 60 C. I'm not too worried about it because I'm probably just going to build a desktop for the monitor, which is why I want to know if the monitor is ok.

Side question: if this is an issue with my laptop, does anyone know exactly what it could be and if there are any fixes to it?

Thank you for taking the time to read my post!

Edit: Here's a screenshot of another black line taken with snipping tool
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