In engineering terms, the "Status MMC Error" indicates that the (the very first code that runs on your Mediatek CPU) successfully initialized, but when it tried to read or write to the eMMC chip , it received a failure response from the hardware.
Let me know your exact device model and firmware version for more targeted help. sp flash tool status mmc error
Many modern MTK devices require a specific to "handshake" with the hardware. In engineering terms, the "Status MMC Error" indicates
A more serious error indicating that the eMMC chip has reached its end of life or is physically damaged. In engineering terms