Just had the same issue on Big Sur. 27" iMac 2017 3.4 Ghz i5, 8GB model. Xcode 12.4
Fixed it by creating a new playground Selecting macOS instead of iOS. Save File Name (example1.playground)
I can confirm that choosing iOS instead of macOS is the issue, as I created another iOS playground and it doesn't run.
Hope this helps!
rrabayah
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