IconComposer alternative app icons not working

I migrated all our alternative app icons to IconComposer icon files in my Xcode 26 project, but calling setAlternativeIconName fails with an error. Also, supportsAlternativeIcons returns false.

This seems like a regression from Xcode 16. Do I need to add the CFBundleAlternateIcons? It's not needed as of Xcode 13 though.

IconComposer alternative app icons not working
 
 
Q