SwiftUI open source

App Development Android Studio is available for free, you can develop app there and launch them on your own devices without any fee. However, Xcode needs $99 per year for app development and deployment on the devices .

Getting Started with Swift on Android. The Swift stdlib can be compiled for Android armv7, x86_64, and aarch64 targets , which makes it possible to execute Swift code on a mobile device running Android or an emulator.

Potentially yes because Android runs on what is essentially Linux, and you could build a compiler for the Android operating system.