If none of the above steps work, your eMMC chip is likely physically damaged or has reached its end of life. Signs include:
Leo added to his internal wiki:
If the error occurs during a “Download Only” or “Firmware Upgrade” operation, try: sp flash tool status mmc error
Ensure the preloader you are flashing is not the cause. If none of the above steps work, your
) that specifically matches your device model if the default one fails. Use "Firmware Upgrade" Mode sp flash tool status mmc error