I'm getting following message when launching #Playgrounds canvas with Xcode 26 beta 4. Here are things I've tried: Reinstall Xcode Reinstall components Removed derived data Run Disk Utility to fix permissions Tried to change Default Actor Isolation, Approachable Concurrency Changed around settings on Schemes: Run: Options and Diagnostics Created brand new project with default settings. Filed FB19003005 in Feedback Assistant. I'm surprised to see that I didn't see any posts on this during my search. So this could be isolated matter just to me.