Resolving a "Simulator runtime is not available" error

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Some Macs recently received a macOS system update which disabled the simulator runtimes used by Xcode 15, including the simulators for iOS, tvOS, watchOS, and visionOS. If your Mac received this update, you will receive the following error message and will be unable to use the simulator:

The simulator runtime is not available.
Code: 401
Failure Reason: runtime profile not found using "System" match policy
Recovery Suggestion: Download the simulator runtime from the Xcode 

To resume using the simulator, please reboot your Mac. After rebooting, check Xcode Preferences → Platforms to ensure that the simulator runtime you would like to use is still installed. If it is missing, use the Get button to download it again.

The Xcode 15.3 Release Notes are also updated with this information.

Up vote post of edford