playgroundRender.swift

import PlaygroundSupport
import SwiftUI
extension UIView {
  var renderedImage: UIImage {
    let image = UIGraphicsImageRenderer(size: self.bounds.size).image { context in
      UIColor.lightGray.set(); UIRectFill(bounds)
      context.cgContext.setAlpha(0.75)
      self.layer.render(in: context.cgContext)
    }
    return image
  }
}
extension View {
  var renderedImage: UIImage {
    let window = UIWindow(frame: CGRect(origin: .zero, size: CGSize(width: 320, height: 160)))
    let hosting = UIHostingController(rootView: self)
    hosting.view.frame = window.frame
    window.rootViewController = hosting
    window.makeKey()
    return hosting.view.renderedImage
  }
}

Text("Hello").renderedImage

Slider(value: .constant(0.5)).renderedImage
let img = ([Color.red, .orange, .yellow, .green, .blue, .purple]
  .reduce(AnyView(Text("👭").font(.largeTitle)
    .rotationEffect(Angle(radians: .pi)))) {
      AnyView($0.padding()
        .background($1)
        .rotationEffect(Angle(radians: .pi / 6)))
}).renderedImage
img

Well, on Catalina I can do this. I haven't tried Mojave.

let view = ([Color.red, .orange, .yellow, .green, .blue, .purple]
    .reduce(AnyView(Text(":-)").font(.largeTitle)
        .rotationEffect(Angle(radians: .pi)))) {
            AnyView($0.padding()
                .background($1)
                .rotationEffect(Angle(radians: .pi / 6)))
})

PlaygroundPage.current.liveView = UIHostingController(rootView: view)

but I see you already know how to do that: https://ericasadun.com/2019/06/06/good-things-swiftui-on-mojave-in-ios-playgrounds/

But on the other hand I got to execute some swiftUI for the first time. Thanks!

(You can’t conform View and if you conform the individual types, it doesn’t work.)

Maybe it's because it's a later beta, but for me this code works perfectly fine in Mojave: