It's not working for me either.

I found that when you toggle off enable results the playground runs successfully without the need to provide a frame modifier. macOS 11.2.1 - Playgrounds 3.4

I tried opening other projects from the direct project file, Xcode would try to open, the project window would try to load, but then it crashes. I reverted the original project to the previous snapshot on git and Xcode opened the project normally. I lost the changes but at Xcode is opening now.