I would contend shipping native code on any mobile platform for a calendar app is overkill, personally.

I did not succeed yet and iOS was indeed holding me back to use Java (or Kotlin, my preferred JVM language). Since a few weeks I've ditched my iPhone because of to the upcoming CSAM scanning changes and I'm back on Android.

By dropping iOS as a requirement, Kotlin/JVM is feasable again for all my personal target platforms and I've decided to use that as the main language for my system.

Codename One has support for an iOS target, from what I can see. Even if it wasn't supported on one platform, it hardly would make Java a legacy language.

Only as paid third-party thing IIRC. But that's still going to be orders of magnitude easier than shipping something in Rust for iOS.