Your Mac mini 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: Your Mac mini storage drive 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 system to an external source. You can set up Time Machine or another back up plan to regularly back up the contents of your computer. See About Startup Security Utility.
Learn more. See the Apple Support article Mac computers that have the Apple T2 Security Chip.