A recovery diagnostics file is generated while the Mac is running in macOS Recovery and can be requested when submitting diagnostic information, such as through Feedback Assistant. Apple’s macOS Recovery documentation instructs the user to connect an external storage device before generating the recovery diagnostics file. After the diagnostic process completes and the screen flashes, a dialog appears that allows the file to be saved to a location on that external storage device. Therefore, option C is correct. Locations such as `/Users/Shared` and `/var/root/Documents` are not the documented destinations for this Recovery workflow, and “Macintosh Data” is not the prescribed storage target. External storage provides a practical way to preserve and transfer diagnostic information when the normal macOS startup environment may not be available.

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