[happytoexplain]

This is only true for the very simple cases you might see in an example snippet. If you need a UIView because you need access to some kind of imperative action (which is usually why you need a UIView), there is no channel for that. Declarative vs imperative are fundamentally incompatible when in the same abstraction layer. You have to use the kind of hacks you used to only see in "bad" codebases, like notification broadcast instead of delegated function calling.

[fingerlocks]

Not sure I follow. Have you seen UIViewRepresentable? You can turn a UIView into a SwiftUI view in 5 lines of code. If you need to move state there is a two way bridge you can choose to implement called a Coordinator. It is a blank protocol with zero obligations to fulfill and only exists as convenient a reference type simultaneously accessible by both the UIView and the SwiftUI parent.

I can’t imagine how it could be implemented more simply.

Even if you are rendering a complex chain of compute shaders with multistage heap fences onto a process shared IOSurfaceRef with several concurrent threads greedily realiasing your scratch buffer to queue up more work, it doesn’t matter. Eventually you’ll up with a UIView or CALayer and it’s still just one function call to bring it into SwiftUI.