I think the Swift compiler does less magic for SwiftUI. They added a new literal syntax for the UI view tree literals, but other than that I believe the behavior is in the runtime. SwiftUI expects you to use Combine, Apple’s (F)RP system, to a greater extent than Compose expects you to use RxJava/Kotlin Flow. My impression is that Compose is more React-y and is actually an escape from RxJava FRP-land; I can translate most hooks to Compose after reading the Compose docs a few times but find it much harder to do the same with SwiftUI/Combine.

Personally I prefer Compose because it’s open-source (so you can figure out how it works if you need to), has much better docs, and seems less welded to FRP stuff which I don’t enjoy. I don’t really have enough experience to really review either though.