Ask HN: Best resources for learning UIKit APIs?

I'm currently making an app using SwiftUI. Though it's mostly fantastic, there are times I need to access UIKit. I've gotten by so far, but I feel out of my element if I want to leverage this technology more. Because the official docs are sparse in examples, I was wondering what are some good resources that I can refer to instead?

* I'm looking for resources that are technically moderately advanced, rather than beginner level tutorials and so on. Thanks!