Are you using Zorin OS 16 or Zorin OS 17?
If on Zorin OS 17, are you logging in on Wayland or X11?
Which Nvidia card are you using and which Nvidia driver are you on?
Do you have Intel integrated graphics alongside Nvidia dedicated graphics or are you solely on Nvidia graphics card?
Have you tried the newmode and addmode commands?
xrandr --newmode "3840x2160_120.00" 1498.55 3840 4192 4616 5392 2160 2163 2168 2316 -hsync +vsync
xrandr --addmode DP-0 3840x2160_120.00