Artifacts only in BIOS and during Windows boot, most likely caused by monitor

[Hpst]

I've noticed that about a week ago weird artifacts started appearing on screen during windows boot and in BIOS. They only occur when the PC was turned off for at least a couple of minutes and appear also on monitors OSD settings. They always disappear before windows boots to the login screen. I think I've already tried everything, plugging different HDMI/DP cables to differnet ports (both on GPU and MOBO), I reset the monitor, BIOS, cleared CMOS, enabled CSM and disabled full HD display in BIOS settings, flashed new BIOS. My monitor is AOC24G2SPAE/BK.
That's how it looks like

https://imgur.com/a/MMX5mYQ

View: https://imgur.com/a/MMX5mYQ