Application build target is above ios 10.3 and simulator is also above ios 10.3 still not supported to change to alternate app icon. The list of Alternate icon names show in Bundle.main.infoDictionary.
supportsAlternateIcons indicates False even though build target is above iOS 10.3
Found the solution: Build on intel chip mac. I built on M1 mac, Xcode 13 hence this feature was not working and the value was set to false by default.