I have had this issue for a while now. I submitted feedback to Apple. Within a few days I got a reply that it should the fixed in Xcode 12.5 beta. I checked, and it's indeed fixed. Hopefully it will stay like that for now.

Hello, @eskimo I have the same problem in the latest Xcode version. I have tried all the steps you provided to see if it is user related. Some I know also tried a completely different playground file on his Mac, without succes. Do you maybe have some more ideas how I can fix this?

This bug has been fixed in Xcode 12.5.