Kotlin Multiplatform + Compose for UI.

I believe YakiHonne is flutter-based and afaik were one of the first Nostr clients to be Multiplatform from the start

Flutter is older and basic multiplatform works. KMP is the future (google has stopped funding flutter) but the iOS part is still VERY new. It works, and it goes native in iOS too, but not everything is perfectly the same as a native UI in iOS. KMP works better for the backend of the apps. I saw ...

WaterUI (Rust) is a new option, and it looks promising. I think I'll use it for the Coop mobile app https://github.com/water-rs/waterui

I think Kotlin Multiplatform with native UIs is a completely different beast than if you use the new Compose Multiplatform UI framework. In general I think Flutter will help you build faster because the UI libraries and tooling is very mature. Google cut a few developers when they moved more Flutter...