Question about AOC C27G2ZU/BK

Unfortunately, I don't know exactly what kind of HDMI cable is included with the monitor, so you'll have to test it yourself. However, an HDMI 2.0 cable (or a DisplayPort 1.2) is required so that the 240Hz can be achieved:

Lindy HDMI (Type A) - HDMI (Type A) (3 m, HDMI)

You need a DisplayPort 1.2 and you have to check if the 240 Hz are activated. On your PC.