Security features on your 27-inch iMac
Your 27-inch iMac includes the Apple T2 Security Chip, which provides the following security features to protect what’s on your computer and prevent unauthorized software apps from loading during startup:
Secure storage: The storage drive of your 27-inch iMac is encrypted with hardware keys to provide advanced levels of security. In the event of a catastrophic failure, data recovery may not be possible, so you need to back up your files to an external source. See the Apple Support article About encrypted storage on your new Mac. You can set up Time Machine or another back up plan to regularly back up your files on the computer. See Back up your files with Time Machine in the macOS User Guide, and the Apple Support article Back up your Mac with Time Machine.
Secure boot and Startup Security Utility: Support for secure boot is turned on automatically. It helps ensure that only legitimate operating system software loads on your computer at startup. See the Apple Support article About Secure Boot.
If your 27-inch iMac doesn’t start up because it detects an untrusted component, it will start up from a secure recovery partition and automatically correct issues if possible. To learn more about the Startup Security Utility or to find out how to set other options, such as starting up from an external device, see the Apple Support article About Startup Security Utility.
Note: In rare circumstances, such as a power failure during a macOS upgrade, your 27-inch iMac may become unresponsive and the firmware on the chip may need to be revived. See the Apple Support article Revive or restore Mac firmware in Apple Configurator 2.
Learn more. See the Apple Support article About the Apple T2 Security Chip.