most monitors these days refresh their screens 60 times per second (aka a frequency of 60 hz). this is a good thing, as for most people, a screen refresh rate of 60 hz is enough for a screen to appear stable. which is to say, the screen should not have any noticeable flickering (which would be annoying!). this happens because near this frequency, the brain's visual processing center, the visual cortex, physically isn't fast enough to process such rapid visual information. if the refresh rate were below 60 hz, the visual cortex would have an easier time processing the flickering, as there would be a longer delay between each refresh. and for reference, the time between each refresh at 60 hz is about 17 msec.
but what if for you, the screen still seemed to flicker even at 60 hz? well, depending on how bad the flicker happens to be, the flicker itself would be only a minor annoyance, because after a certain amount of time, your brain would just get used to the flicker, causing a reduction in the flicker. this is similar to how we ignore seeing our nose, even though our nose happens to always be present in your vision...
but would the flicker itself cause any strange side effects, like the hypnotizing, attention-stealing effect you've been describing? well... something kind of like it, actually. since the human brain uses pulse-density modulation to synchronize the different parts of your brain. in this way, the human brain is sensitive to brainwave synchronization if presented with a periodic stimulus. since a brainwave with a frequency of 60 hz is a gamma wave, and gamma waves are associated with heightened attention spans and awareness, it's possible that by synchronizing your brain to gamma waves, you'll also experience these effects. but these effects i'm describing are contradictory with what you're describing.
also these effects would be minor at most, as 1) the human brain is most sensitive to gamma waves of 40 hz, 2) flickering has already been substantially reduced at a refresh rate of 60 hz, and so wouldn't be noticeable, and 3) brainwave synchronization would be isolated to the visual cortex, and would have less of an effect to other parts of the brain.
so at worst you'll probably get some fatigue and a possible headache if you stared at the screen after awhile. and what about your other issues? well, blue light from the screen doesn't harm your attention span... if you're using that time on the computer productively, it should actually boost it. and temporal dithering is just another form of noise. if the dithering is done right, at a high enough refresh rate, the brain shouldn't be able to interpret a noticeable pattern in the noise or notice the noise at all.
but if the monitor's refresh rate isn't the problem, then what's causing the problem for you? the simplest explanation, and probably the most probable, is that you've conditioned yourself to waste time on the computer, the tv, and your smartphone. in other words, a neural feedback loop in your brain caused by spending too much time on 4chan is what's causing you to lose focus>>7, >>4,