iOS/tvOS playground fails with "Unable to find execution service for selected run destination"

There may be a faster solution:

Check that you have iPad Pro simulator in your devices in Xcode. If not – add it via Add Simulator option.

As some have noted in comments, you may also need to restart Xcode or reopen the playground.

To add a simulator go to Devices (Window > Devices). Click the + button at the far bottom left of the window, click "Add Simulator", then select the appropriate "Device Type" from the dropdown and click "Create".

Ok, after some struggle, here's the solution.

1. Clean up the folder ~/Library/Developer/CoreSimulator
2. Restart the machine
3. Try running an iOS Playground, it should work without problems now.

Note: In my case I renamed CoreSimulator to CoreSimulator.old, and after restart a new CoreSimulator was auto-created (so, I just threw away the .old one).

BTW, there is a file ~/Library/Developer/CoreSimulator/Devices/device_set.plist with whole list of Simulators under /Root/DefaultDevices. I think this is where the problem was coming from.

I was able to resolve this issue with these two commands in the Terminal:

$ rm -rf ~/Library/Developer/CoreSimulator/Devices$ killall -9 com.apple.CoreSimulator.CoreSimulatorService