The iOS 13.0 simulator runtime is not available
CoreSimulator does not currently like simruntime bundles being moved out from under it. By launching from ~/Downloads it became aware of the iOS.simruntime for iOS 13, then you moved it.
In this one specific case you can workaround the problem by killing com.apple.CoreSimulator.CoreSimulatorService.
Weird thing is I wake up in the morning and start my computer, the Canvas and the iOS 13.0 Simulator can work now.
So, I guess the solution to this may be just a brutal restart. ;]
The XCode 11 upgrade breaks simulators in a weird way that I don't fully understand - nothing I tried would work to get simulators to run after the upgrade, and I couldn't find much in the way of clear answers as to why that was the case, but the following two commands fixed the issue for me:
sudo xcrun simctl shutdown allsudo xcrun simctl erase all