Diagnosis
Windows is defaulting to a basic display driver because it's not receiving the correct capabilities data from the monitor. This is almost always a cable or connection issue, not a monitor defect.
How to Fix It
Follow these steps in order. 1) Cable Check: You must be using the DisplayPort cable that came in the box, or a high-speed HDMI cable (HDMI 2.0 or later). Older HDMI cables won't cut it. 2) Connection Check: Ensure the cable is plugged into your graphics card's output, not your motherboard's. 3) OSD Check: On the monitor, open the OSD with the joystick, go to the Gaming menu, and ensure 'Overclocking' is set to 'On'. This enables the 165Hz mode. 4) Driver Check: Make sure your graphics card drivers are fully updated from Nvidia or AMD's website. 5) Windows Settings: Now go to Windows Settings > System > Display > Advanced display settings. Click 'Display adapter properties for Display 1', go to the 'Monitor' tab, and you should now see 165Hz in the 'Screen refresh rate' dropdown.
If That Didn't Work
If you're using an HDMI cable and 165Hz still isn't showing, the monitor may need to have its 'Overclocking' setting turned on first via the OSD before it will advertise the higher refresh rate over HDMI. Also, some older graphics cards (pre-10-series Nvidia or pre-RX 400 AMD) may not support 165Hz at 1440p over HDMI.
Heads Up
If you enable 'Overclocking' in the OSD to get 165Hz, there's a very small chance you might see minor screen flickering. If that happens, just drop the refresh rate to 144Hz in Windows settings—it's still incredibly smooth and is the monitor's native refresh rate.