Hello Kenta,
I have test it use the MULTILINK , it can work well .
- Please first change the bootloader of the board , for example , you can change it to jlink
use the "JLink_OpenSDA_V2_1.bin" .
- then connect the board ,debugger to PC :

then check the PC management , whether have the USB Multilink:

Then configure the debug configuration as this :

Then it can download well :

Hope it helps
Have a great day,
Alice Yang
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