Change display settings in Windows with Boot Camp on Mac
In Windows on an Intel-based Mac, you can adjust settings for your external display or change the brightness of your built-in display.
Change your external display’s settings
Depending on the model of your external display, you may be able to set the brightness level and turn automatic brightness adjustment on or off.
If you have an Apple Pro Display XDR, you also see the Presets pop-up menu, which you can use to choose a reference mode. See the Apple Support article Use reference modes with your Apple Pro Display XDR.
In Windows on your Mac, click
in the right side of the taskbar, click the Boot Camp icon 
, then choose Boot Camp Control Panel.If a User Account Control dialog appears, click Yes.
Click Display, then choose the desired settings.
Change your built-in display’s brightness
You can adjust your built-in display’s brightness in Windows or with the brightness keys on your Apple keyboard.
In Windows on your Mac, do one of the following:
Use Windows: Click the Start button, choose Settings, then click System. In the list on the left, click Display, then set brightness options as desired.
Use your Apple keyboard: Press the increase brightness key
or the decrease brightness key 
.Note: You may need to press and hold the Fn key as you press the brightness keys. For information about configuring the Fn key, see Use Windows keys on a Mac keyboard.