Can't understand monitor differences and prices, eye strain (Acer XV282KKV)

Spyrex

I just bought a new 4k monitor for programming and some casual gaming: The Acer XV282KKV Xbox Edition. With 500€ it was quite cheap. The monitor is good, but my eyes instantly hurt when reading text, that's why I will return it. It basically feels like looking at a Psychedelic Pattern image.

I tried the Acer Predator X28 at a tech store and reading felt great. It costs around 800€ but has nearly the same specs.

Doing some research I found the Acer Predator XB283KKV which looks nearly the same as the X28 but is just 650€.
According to this website they are all nearly the same but I know that the cheap one is making my eyes explode and the expensive one feels like eye candy.

Now I would like to know what is causing this pain and what to look out for when buying one of these. Should I buy the 650€ one or the 800€ one? These same specs are driving me insane.

[Edited the thread to add model number to the title and to add issue detail]

Puraw

https://community.acer.com/en/discussion/702008/cant-understand-monitor-differences-and-prices-eye-strain

PWM Dimming can cause eyestrain: https://www.eizo.com/library/basics/eyestrain/ and check this link: https://www.visioncenter.org/conditions/digital-eye-strain/

Spyrex

https://community.acer.com/en/discussion/comment/1264180#Comment_1264180

Okay, but how do I know, what monitor I can buy and which ones will/could hurt? All monitors I mentioned have the same "eye-care" technologies and are advertised as flicker-free but they feel different for my eyes and there must be something causing the big price range.