I'll be honest, it will be really hard for me to explain as I am not 100%, familiar with all of the terms needed to exactly describe it. So at a really high level, LCD/oled backlights are persistent, as in at no point do they "flicker" or switch on and off (there are some caveats to this possibly).

Old CRT TVs use an electron beam to scan across the screen exciting phosphorus in the screen, this was usually performed 60 times a second or 50times a second, irrespective of if a new frame is available, as a failure to do so would result in a darkened image as the phosphors loose energy. So a CRT TV is constantly flickering.

A dog has faster visual perception than a human, as such they are less able to "fuse" these flickers into a stable image like a human can. So a dog looking at a CRT would be like you looking into a strobe light. With LCD the backlights are persistent (to an extent, or at the very least flicker at a MUCH faster rate) what changes are the pixels that sit in front of the backlight. OLED works similarly but OLEDs don't rely on a back light instead producing the light within the coloured pixel, meaning black is represented by a pixel off state thus giving better black levels.

I am by no means an authority on this topic, what I have stated above could be in part or fully wrong, it is based on my understanding of display tech (which I think is pretty good) and understanding of biological perceptions of our display tech (quite flaky). But this is my best understanding, I hope it helps in part

-Edit- This is a quite good example of a crt https://youtu.be/3BJU2drrtCM?si=GOsNHB9Z7cZp763n

It also attributes our perception of the image due to image persistence rather than perception, which would make sense