Not a full-fledged library yet, but you might want to take a look at my Builder project to see what's possible with obtaining a SwiftUI-like declarative syntax (including view composition) in UIKit.

https://github.com/hmlongco/Builder

As to SwiftUI, yes it has its own challenges, but it's state-changes, view-updates approach also eliminates a huge set of potential application bugs. You simply have to think about things differently, and above all bind changes as low in the view tree as possible.