Icon Composer: Any way to add icons to the app bundle for older macOS versions?

Ok, I did some digging. According to assetutil it seems like Assets.car contains an iconstack that has all the vector layers, color data etc for the glass icon and the traditional MultiSized Image with all the icon size variants for legacy macOS versions. In beta3 however (probably due to a bug) the MultiSized image variants were not created based on the Icon Composer image (only a single 1024x1024 variant was created). This gave way for the .incs file compiled into the app root to be taken as icon image on legacy macOS versions, which feeds from the proper xcassets icon file provided by the developer, not the Icon Composer generated pngs.

In beta4 this was "fixed", so now all size variants 16x16, 32x32...512x512 variants of the Icon Composer based MultiSize Image items are compiled into the Assets.car file - so macOS takes these now. Sadly there is no way to somehow replace these variants with the proper, developer supplied image or remove them (so the .incs file could be taken by legacy macOS versions instead) - the only tool assetutil that is given to manipulate .car files is extremely limited.

I really hope Apple will fix this. I don't see why it would be beneficial to entirely disregard the developer supplied App Icon asset and instead render (somewhat oddly looking) variants based on Icon Composer icons meant for glass (it should happen only if the developer does not provide custom App Icons suitable for older macOS versions).

An alternate solution would be to improve Icon Composer so it could take icon composition variants for legacy OS versions and the developer (so instead of only "watchOS" and "iOS/macOS" these should be a third "legacy iOS/macOS" option). This could at least enable developers to supply vector and bitmap images that match the legacy icon size/corner rounding. Also there should be a preview option in Icon Composer how the icon would look on older OS versions - the way that Icon Composer now "silently" produces entirely different looking variants for macOS 15 without a developer using Tahoe ever even seeing how it actually looks like is clearly not the right way to go.

Note: I also added an issue about it in case an Apple Developer would kindly look into it and give directions on how to get around this limitation:

FB19118531

Thank you!

I received a note to FB19118531 saying Apple Engineers will look into the issue.

In Xcode 26 beta 5 there is a slight change - now the .incs file also has the icon composer generated icon (under Resources in the app bundle) with the wrong corner radius (that matches older macOS versions), making any icon that relies on the proper corner radius look bad. This means that the developer supplied Assets app icons are entirely disregarded.

I still feel that either if the developer supplies a legacy App Icon, it should be used for older macOS versions both for the .incs file and Assets.car. Or at least have the option to have the icon composer generate icons with the new corner radius even for older macOS versions (imho that does not look out of place as older macOS versions had icons in all kinds of shapes - obviously for iOS this is not a viable solution).

Sadly nothing changed in Xcode 26 beta6 it seems. :(

This solution does worked for me and I hope it will still be working with the final release of Xcode – just in case Apple decides, to never fix this mess.

Amazing! Thanks @superpixel!

Adding the secret undocumented --enable-icon-stack-fallback-generation=disabled to the ASSETCATALOG_OTHER_FLAGS build setting does work on Xcode 26 beta 6.

What I do is enable this, disable "Include all app icon assets" and copy a separately compiled AppIcon.incs (with the legacy icons) to the Resources folder while making sure the CFBundleIconFile is in the Info.plist pointing to this file - this results in the correct icon showing up on older macOS versions, while Tahoe uses the Icon Composer variant. This should work on macOS (not sure if works for App Store, but my app is not an App Store app, so it does not matter).

An other way is to have "Include all app icon assets" which generates the proper variants in Assets.car, but it bloats the bundle size somewhat (especially as I have some assets that depend on build configuration and this option makes all those into the bundle) - this might be the proper way though.

Hope Apple fixes this properly though or add least adds a proper, documented build setting with a guarantee that this (rather hacky) solution won't go away suddenly in a future Xcode update.

Well, I don't know what I'm doing wrong. I'm using Xcode 26 Beta 6 on a macOS 26 Beta 6 VM, with macOS 15.6.1 as the host.

I can build the TahoeIconsTest project, pointed to by @superpixel, and it works just as expected, the LG icon is used on macOS 26 and the old icon is used on 15.6.1. I do note that the .icns and .icon files are not in the app bundle , but there is a .car file. The Info.plist only has CFBundleIconName set (to AppIcon).

However, I'm just not able to replicate this outcome with my own app. I added the "secret" flag and all the other asset compiler options are the same as the test project. But my build has all three files, .icns, .icon, and .car in the bundle, and my Info.plist file has both CFBundleIcon* parameters set to AppIcon. The result is both OSs use the old icon.

I just can't see what's different.

In case it's helpful to anyone else, I managed to get past the problem I was having with the new style icon. It turns out, all I had to do was rename the AppIcon.icon file to anything else (within the Xcode 26 GUI) then rename it back. Apparently, I added the file to the project in Xcode 16, so it wasn't flagged properly as an icon asset.

Later, I had a separate problem with the same symptom. This time I added the .icon file with Xcode 26, but in the dialog, I neglected to check the box for the target, so it wasn't added to the "Copy Bundle Resources" build phase.