iOS app icon with transparent background showing black background on device
From the apple developer website after a quick search:
Avoid transparency. An app icon should be opaque. If the icon’s boundaries are smaller than the recommended sizes—or you use transparency to create “see-through” areas—the resulting icon can appear to float on a black background, which tends to look especially unattractive on the beautiful wallpapers that users choose.
https://developer.apple.com/ios/human-interface-guidelines/icons-and-images/app-icon/
Edit: Also, check the related questions before you confirm your post - Is is possible to use transparency in an iPhone app icon?
On IOS use just square icons, if you use rounder icons you will have black margin black background.