I set the icon in Xcode, but somehow there is a black frame.

The image being used is incorrect as an icon.

It's hard to see when it's displayed on the white background screen, but it looks like this when the background is blue because it uses a transparent color.

Below is excerpt from Apple's Human Interface Guideline

(I couldn't find the Japanese version, so please forgive me.)

Keep the background simple and void transparency.Make sure your icon is opaque, and don't clutter the background. Give it a simple
background so it does not do't overpower other applications learnby.You don't
need to fill the entire icon with content.

Keep the background simple and avoid transparent colors. Make sure the icon is opaque and do not mess up the background.Simplify the background to avoid unnecessary impact on other icons around you.You don't need to stuff every inch of the icon.

Keep icon corners square.The system applications a mask that rounds icon corners automatically.

Keep the corners of the icon square.The iOS system automatically masks the corners of the icon.

Regarding the first background color transparency, iOS does not guarantee what kind of background it displays when displaying icons.The transparent area may have the image displayed around it, or it may just be black as you did in your example, so using transparent colors can be completely unintended and strange, so the use itself is prohibited.

If you can see the black frame so clearly, there is a high possibility that the App Store will not be able to pass the examination due to a defect in the icon (violation of HIG).Please prepare a square icon that does not use any transparent colors and replace it.(Of course, if it is actually displayed, it is necessary to place the contents in the assumption that it will be rounded.)