Mi A2 last version firmware 10.0.8 and 10.0.5 have a big bug and brick your device.
to resolved this problem follow this tutorial :
important : before flash 10.0.8 firmware or update from phone, you must active oem unlock in developer option
1. after brick your device, enter fastboot mode.
2. unlock your device bootloader by this command : fastboot oem unlock
3. after unlocking your bootloader type : fastboot erase system
4. write 10.0.2 system image by this command : fastboot flash system system.img
5. when done wipe your system : fastboot -w
6. reset your phone and register it.
7. return to fastboot and relock your bootloader : fastboot oem lock
8. this command was wipe your device and boot to os.
done and your device backe to life.
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