The board, marked as DevEBox STM32F407, sparked my interest. You can find it on (Aliexpress)[https://aliexpress.ru/item/4000006334837.html], currently with an about $12 price tag for the VGT6 version (coming with 1024k flash memory rather than VET6’s 512k).

To flash a binary, we should put the controller in DFU mode. Connect the BOOT0 pin (marked as BT0) to 3V3 on the unpowered board, then plug it in via USB and wait until the bootloader gets recognized (it should have the 0483:df11 device ID).

Use dfu-util for uploading:

$ sudo apt-get install dfu-util
$ dfu-util -a 0 -d 0483:df11 -D fw.bin