You can implement the same syntax for a renderer on other platforms but all of SwiftUI is closed source. So the diffing engine etc… all would need to be re-created from the ground up.

SwiftUI, like react uses some language constructs to make it look really fancy but in reality it's really simple nested data structs.

The real hard part is what the "DOM" provides for React and likewise what UIKit/iOS is doing with those data structs.