What causes monitors to flicker?

Question

Iron

Good day. There are two monitors, one at 60Hz, the second at 75Hz. When entering games or cpu/gpu intensive application the monitor flickers at 60hz. I also can’t play without vertical synchronization, I see frame breaks that are noticeable on the main 75Hz monitor. If you need more specific clarifications, ask questions, I will try to clarify what I can.

ATX FRACTAL DESIGN Define C
AEROCOOL Motion 12 plus x3
AEROCOOL Strike-X 600
GIGABYTE X570 AORUS ELITE
AMD Ryzen 7 3800X
AEROCOOL Verkho 4
Patriot Memory VIPER STEEL PVS416G360C7K x2
Inno3D iChill GeForce GTX 1070
TOSHIBA-TR200 x2
TOSHIBA HDWD110
Western Digital WD5000LPCX

ASUS VP228DE
AOC Value Line 22V2Q

Answer 1

I once played one cool game, everything was fine. But a friend came up to me and asked: What is this strange stripe in the center of the screen? After that, I could no longer ignore her, and then she infuriated me until the very end of the game.
And on the topic of flickering, I give a link where you can find a bunch of other links:
https://www.google.com/search?q=From+what+can+flicker...
All kinds of reasons for flickering are listed there.