This is a bit unfortunate, and perhaps poorly documented BUT Apple seems to have started requiring a 1024x1024 application icon to be bundled with the IPA (at least for new applications?).
The only way such an icon can be included is through a stupid proprietary asset format Assets.car file. And the only way you can create an Assets.car file is through Xcode and an intermediary *.xcasset file. This is the same problem as we have with launch screen storyboards.
So, you need an Assets.car file specified in game.project and you need to specify the icon names (because they will be added to your Info.plist and where they are used to reference the actual files in the Asset.car file).
The process is documented here:
Are you using a custom info.plist btw?