Black box on top of screen

yuki1212,

Thank you. As you're still having this issue and the behavior is not appearing in your screenshots, we recommend contacting Apple Support for additional troubleshooting: Contact Apple Support

They can further assist to answer the the question if this is expected or unexpected behavior.

Take care.

Hi yuki1212,

Welcome to Apple Support Communities. From your screenshot, we don't see the black box you're referring to. You may be indicating the dark space at the top in the background. This space should be a blurred background of whatever you use for your Home Screen wallpaper. If you use a darker wallpaper, try changing it using the following guidance from Change the wallpaper on your iPhone - Apple Support and see if the same occurs.

"Add a new wallpaper for your Lock Screen or Home Screen

1. In the Settings app, tap Wallpaper.
2. Tap Add New Wallpaper.
3. Tap Photos, People, or Photo Shuffle to choose your own photo. You can also select a wallpaper from a category like Weather & Astronomy, Emoji, Collections, or Color.
4. If you want, you can customize your wallpaper further. Then tap Add."

Cheers!

Hey there yuki1212, 

Your screenshot appears to show another example of the blurred effect when the App Switcher is open on your iPhone. Do you see a black box when you are not using App Switcher? We ask as there is no black box present in these screenshots, only the App Switcher view. As shown below.

Switch between open apps on iPhone

If you are seeing the box on your device, but not in the screenshots you are sharing, you may need to have your iPhone checked out.

iPhone Service & Repair

Have a good one!