The easiest way to resize your app icons for iOS, macOS and watchOS to use it in Xcode. Looks fine in Light Mode and Dark Mode.
With Xcode 14 you can select your app icons in all sizes or just one size except for macOS, where you still need all sizes. If you are using an older version of Xcode you will need all sizes for your app icons.
App Icon Sizr is the easiest way to convert your app icons in all sizes. Just click on the button to load your app icon from the folder. In the next step, select the operating system you want. Then you can save your app icons in different sizes with the export function on your hard drive.
If you have wishes for improvement, then don't hesitate to write to me. E-Mail: infos@berkantdursun.de