The fastest and simplest way to change the brightness of your iPhone's screen is through Control Center. To open Control Center on an iPhone 8 or older, swipe up from the bottom of the screen.

If you want to change Hyper-V Display Resolution, you must enable Enhanced Session Mode on the Windows system. Read this guide to know more.

There are a few (legitimate) reasons why iPhones decide to change screen brightness. Thankfully, you can turn off all of those features.