Alpha R2 problems with 4K monitor

Hi to all. Recently i bought a 4K monitor ( LG Ultrafine ergo 32") and connected Alpha R2 through HDMI 2.0 port... i know that i can't play any game at 4K resolution but i only want to watch at least a video in that resolution in youtube... by the time i connected to the monitor i discovered that some yellow little squares appeared across the screen when i open for example the Nvidia experience software or a chrome page with white background... i'm i missing something about settings? I did all the updates to drivers and windows updates... is it normal?  Is Alpha R2 not capable of handling 4K resolution for plain windows use? Thanking you in advance for any help...