Thank you for that hint - maybe that is the problem "under the surface". Since Playgrounds does not provide any error message but simply refuses to "preview/run" it might well be that problem. I tried to reproduce in a normal Playground on a Page and there I can easily combine UIKit, SwiftUI and PlaygroundBluetooth. So I guess that has something to do with the AppPlayground Environment.

Thanks for the quick reply. I ran through the tutorials you mentioned and I understand, I need to extract that from the view - so I did. In Swift Playgrounds, I added another file containing a single class with just the a declaration: import PlaygroundSupport import PlaygroundBluetooth class ConnectionHandler {     //var centralManager: PlaygroundBluetoothCentralManager? } There is no link between a UI-Element and that class - just an additional Code-Snippet. And that reproduces the problem - when I uncomment the declaration, playgrounds won't compile/start the app. Unfortunately, there are no error messages/warnings/whatever. Is that maybe a principle problem with Apps in Playground (not in Xcode)