AshX If dithering is present in a video capture, then we know where at least part of the problem lies (but I do not believe its absence proves that the signal is clean). And yes, flickering can be introduced downstream of that. Also, a GPU is not guaranteed to send the same signal to the capture card as to an actual monitor, although EDID emulation is a feature of some capture cards.
I am not too familiar with analyzing for dithering with a microscope and camera, although I see others here claim that this works. I would be concerned that regularly occurring camera sensor noise, image processing, and other physical factors such as pixel inversion, can introduce barriers. On the other hand, I have seen dithering so obvious that I could see it with the naked eye, and I did use a camera to record it in those cases.
I think most ideally, we would want to analyze the (eDP?) signal going straight into the panel, from the logic board of the laptop (or of an external monitor). I am not sure what kind of equipment would be needed for this.
Edit: simplex I think I still have all of the captures from these cards: https://ledstrain.org/d/703-i-have-bought-a-capture-card/53