fresh rate discrepancy b/w my monitor's spec and that from ubuntu display settings

when I tried to reconfigure the display settings on my ubuntu 20.04, I noticed that the highest fresh rate is 30HZ (I couldn’t upload the screenshot due to this site complaining it failed to connect to imgur).

When I checked my Viewsonic monitor’s spec, I noticed the highest rate it supports is 60HZ.

Why is the discrepancy? it looks like that Ubuntu failed to exploit the monitor’s potential. My GPU is Nvidia RTX 2080 Super.

I don’t know too much about fresh rate – my take is that the higher the better, reducing flickering, and is an important spec especially for gaming.