+1
I think it's a useful change for people who use Redmine from iPhone.

With the addition of apple-touch-icon, the icon when a web page is added to the home page on the iPhone will change.
https://developer.apple.com/library/archive/documentation/AppleApplications/Reference/SafariWebContent/ConfiguringWebApplications/ConfiguringWebApplications.html

The icon to the right of the screenshot below was created after applying the patch for this issue. In the current Redmine, the icon on the left is created.
!{width: 200px; border: 1px solid #ccc}IMG_9A459A7A8252-1.jpeg!
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+1 It improves Redmine's usability on mobile (Apple) devices.
I'm not a fan of the attached icon but that's a matter of taste and shouldn't be a deal breaker.
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This change will also change the icon when you press the Share button or the Add Bookmark button.

!share-screen.jpg!
!add-bookmark-screen.jpg!

If you make the png transparent, this is what it will look like in dark mode

!add-bookmark-screen-darkmode.jpg!
!home-screen-darkmode.jpg!

This patch uses the images in /public/theme/touchicon if they are available, so you have more flexibility in your theme
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