Why is it recommended that "don't provide app icons in ICNS or JPEG format."

Below url, it is written "Don't provide app icons in ICNS or JPEG format."

https://developer.apple.com/macos/human-interface-guidelines/icons-and-images/app-icon/


I have a question about why it is not allowed about .icns.


My previous macOS app's app icons is in a icns file. is there any potential problem?

How long ago is 'previous'?

Why is it recommended that "don't provide app icons in ICNS or JPEG format."
 
 
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