As far as I understood, you want to flash the images on the embedded emmc. For that purpose, you should use the FlashLayout_emmc_optee.tsv file. The clear is only to reset the emmc as Android can't be flashed on emmc and on sdcard at the same time (conflict between partitions with the same name).
Well I don't really understand what I'm doing wrong. Because I'm using the EVAL board, I've got the ST-Link USB (CN4) connected, the USB OTG (CN16) connected, the BOOT pin are on OFF (DFU), and JP4, JP5 so that the serial goes to the ST-LINK.
I just want to flash the eMMC and I've downloaded this "st-android-9.0.0-2019-09-27-eval-emmc-starter". There is 2 TSV files: the "..._clear.tsv" and the "..._optee.tsv",
This this the number I expected. It confirms that your board has been provided through specific partner program. It is no more supported (old version).
I suggest you to contact your official contact to exchange your board with the latest one. You must have a MB1263C board.