Android hardware utilizes a secure chain of trust starting from the bootloader. If you attempt to use commands like fastboot flash boot boot.img while this chain is active, the device rejects the command with a protection error. The primary causes are:
You must download the Mi Unlock Tool on a PC. flashing lock flag is locked please unlock it first full
The error is a multi-contextual warning that always points to three simultaneous conditions: Android hardware utilizes a secure chain of trust