About brightness levels
iOS devices use an ambient light sensor to adjust brightness levels based on the light conditions around you. The sensor lowers brightness in dark locations and raises brightness in light locations. The auto-brightness feature is on by default.
When auto-brightness is on, you'll notice that your device's brightness slider moves according to changing light conditions.
In iOS 11 and later, you can turn auto-brightness on or off in Settings > General > Accessibility > Display Accommodations.
iPod touch doesn't support the auto-brightness feature.
Learn more
* You can use True Tone with these devices: iPhone 8 and later, iPad Pro 12.9-inch (3rd generation), iPad Pro 11-inch, iPad Pro 12.9-inch (2nd generation), iPad Pro 10.5-inch, iPad Pro (9.7-inch), iPad Air (3rd generation), and iPad mini (5th generation).
Adjust the brightness on your iPhone, iPad, or iPod touch - Apple ...
https://support.apple.com/en-us/HT202613
If the above does not help take your device to an Apple Retail Store or Apple Authorized Service Provider, or contact Apple Support:
Apple Repair and Repair Status Check - Official Apple Support
https://support.apple.com/repair
Apple Authorized Service Provider
https://locate.apple.com › Home › Find Locations
Find Locations - Location Selector - Apple
https://locate.apple.com › Find Locations
Contact Apple for support and service - Apple Support
https://support.apple.com/en-us/HT201232