DIAGNOSIS Windows is using a generic display driver, not the monitor's native capabilities. You haven't enabled the high refresh rate in both Windows AND your graphics card control panel.
FIX Go to Windows Settings > System > Display > Advanced display settings. Click 'Display adapter properties for Display 1'. In the new window, go to the 'Monitor' tab. Your 'Screen refresh rate' dropdown should now show 144Hz and 160Hz options. Select 160Hz and apply. If you only see 60Hz, you must also open your NVIDIA Control Panel or AMD Radeon Software. Under 'Display' > 'Change resolution', manually set the refresh rate to 160Hz. This overrides the Windows setting.
IF THAT DIDN'T WORK You are likely using the wrong cable or port. The 160Hz mode requires the use of a DisplayPort cable. The included HDMI cable may only support 144Hz at 1080p. Purchase a certified DisplayPort 1.2 (or higher) cable and connect it.
HEADS UP Some game launchers and in-game settings have their own frame rate caps. After enabling 160Hz system-wide, go into your game's video settings and set the FPS limit or refresh rate to 160Hz there too.