Thank you for the advice!

Unfortunately I’ve tried a number of very expensive cables, as well as multiple graphics cards. The monitors used to be fine, but over time they started getting all these horizontal lines across the screen if I go above 100hz. I’ve also tried Mac and Windows and same problem with both.

I’ve looked it up though and seems to be a common problem for AOC Agon monitors, so my fault for cheaping out, even though they still cost me $550aud per monitor :(