120Hz is specifically used if you connect the monitor via HDMI, I'm using DP cable. As you can see from the video in the game I changed the resolution, and everything downscale (as for graphics) but after changing the resolution, it blinks black after even though I changed the resolution to 2560x1440 it says Display port 3840x2160.
At widows desktop, if I change the resolution to 1440p it works with 144hz with no problems, the problem persists only in-game, although I have an old game "Darsiders 2" when I change the resolution to 1440p in blinks black screen and says Display port 2560x1440 and it works with 144hz, other games just even though I change the resolution to 1440p it stays 4k 120hz...