App icon design file format and size requirements

See the HIGs - start here:

https://developer.apple.com/ios/human-interface-guidelines/graphics/image-size-and-resolution/

Naming/sizes - Tech OA1686:

https://developer.apple.com/library/content/qa/qa1686/_index.html

Sample app:

Application Icons and Launch Images for iOS

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Tags: Human Interface Guidelines

A pixel is a point. Therefore, if you look at your AppIcon asset it will label what you need. For instance, for iPhone App iOS 7-10 you need 60pt, which will be 60 pixels. However, you will need to versions of that image. One that is 2x and 3x, meaning you will need an image that is 120px and 180px. You can do that simple calculation for all the required slots.

I'm assuming in PS>Export As>Scale All>@1x, @2x, @3x...to generate and save all file sizes without having to save each individual size?

I'm operating without any of the fancy stuff you guys have. I just use Apple's Preview program and adjust the size based on "pixels".