An error appears (Thread 1: Fatal error: Unexpectedly found nil while unwrapping an Optional value) when I try to add a scene file with the .sks extension to an app playground type project with the .swiftpm extension

Hi and happy new year!

The error indicates that the file wasn't found - the app usually searches the file inside the Resources folder.

I am not sure if moving it inside the Resources folder inside GamePlayground would work. If it doesn't, try adding the scene again so that a "global" Resources folder is created (either drag & drop the scene or click the plus button in the bottom left.