Probably not a feature-complete app, but they're not completely unable to code Swift apps. I wanted to contrast Claude vs Codex and had both build a basic weather app just to see if they could. It wasn't anything anyone would want or buy, but they were both able to do that much.
I've successfully spec-coded a functional iOS terminal app for proxying Claude Code (and family) from an owned system. It was easy - even the icon and slick splash screen.
An Apple Developer Account would be required to deploy it. A free account permits sideloading of a private app.
Probably not a feature-complete app, but they're not completely unable to code Swift apps. I wanted to contrast Claude vs Codex and had both build a basic weather app just to see if they could. It wasn't anything anyone would want or buy, but they were both able to do that much.