Automatic brightness, but it will still dim when entering the app.

This is not a problem of a certain brand of mobile phone, Android and Apple may appear. If individual apps turn black when opening the screen, it may be because transparent wallpaper is set in the system. Transparent wallpaper is only valid for activated apps, so those apps will turn black as soon as they are opened. Just go to the theme wallpaper-My Cool function, close the transparent wallpaper, or close the activated app in the transparent wallpaper. I am a Xiaomi user, and Android and Apple phones such as Huawei will have similar problems. If you can't find transparent wallpaper due to different mobile phone brands and different settings, you can look at the tutorial on setting transparent wallpaper online.