Not "DFU" as in an implementation of the USB DFU 1.1 class, but a hardware boot ROM with spiritually the same mechanisms exists.

It's literally a ROM. You can't overwrite a ROM. There's no flash or EEPROM on the chip at all.

You don’t understand. If there is no DFU the next application cannot be fixed if it broken. Hence bricked. If the boot rom goes right to the sd card image then there is no problem.

Almost all embedded devices have a secondary boot loader.

Do you understand my question now?

Sorry, misread your question.

Yes, it has a DFU on the boot ROM.

Ahh... thank you.