Try opening it in Xcode. Apps created in iPad Playgrounds4 (with a file extension *.swiftpm) can be opened in Xcode 13.2. But if you haven't already updated to Xcode 13.2, see the comments in the Xcode forum; there are some problems with the Mac App Store version.

Just in case anyone else makes the same mistake I did. When adding the Bundle Identifier under Signing & Capabilities, somehow I had added it to the iOS section, but not to the field directly under Team (maybe because I added the BundleID before changing the Team to me?). I noticed this after reading through this post and going back to check if I had everything correct. I saw that there were 2 Bundle Identifier fields and the top one still had the Apple sample project BundleID. When I copied my BundleID to the field underneath Team, everything started working (& the 2nd Bundle Identifier field in the iOS section just disappeared).

I think this requires adding @Bindable to the appData declaration. @Bindable var appData:AppData This is from WWDC23 "Discover Observation in Swift" 6:27

I'm not sure if the timing was just coincidental, but I had the same problem and after I quit & re-opened Xcode I was able to download the iOS Simulator.

I had the same problem (& tried the same cleaning/deleting steps) when I first installed Xcode 16 beta 2. It only occurred in a project that I had created using Xcode 16 beta 1. I never could figure out what was causing it. I ended up just re-creating the project fresh in beta 2 and that worked. Luckily it wasn't a very big project. I copied over most of the code files as-is from the crashing project, so I suspect Xcode was just "confused" about something in the project file.