240hz not showing & black screen every time i move my mouse on 120hz?

Not sure what is happening but I have a 4K 240hz OLED monitor and 240hz doesnt show up in the display options. 120hz does show up but for some reason literally every time I move my mouse it black screens for like 1-2 seconds only on this monitor. Doesnt happen on my other side monitor, and that one did have 240hz show up(its 1440p 240hz)