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

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.

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.