I have installed Playground 4 on both iPad and Mac. My iPad is an iPad Pro and my Mac it’s s MacBook Pro Intel. I do can add an app in Playground for iPad, but not in the Mac. does Playground 4 has some limitation for M processors only, and it is not 100% compatible for Intel macs?
I am also having this issue. I think that you can only open app projects on Macs if they have an Apple processor, but it would be nice if this could be confirmed.
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.
XCode it’s not an option for my MacBook, it just claims too much disk space. The option to have Playground 4 with a minimum development capability in my Mac, as in the iPad, was a very interesting feature. Well I’ll keep using Xcode on the Mac mini and playground on the iPad.