I see. Let’s eliminate some variables and make it minimalistic.
I’ve update the repo to incorporate the fix in the board definition. Additionally I overlooked some stuff in the linker script that the STM32Duino linker scripts do, and I’ve fixed those.
I’ve stripped down the code to do only LED flashing and replaced the clock init function with one that just starts up from the internal HSI oscillator, to eliminate problems when try to use the external crystal on the board. USB will not work with this, but it should be well enough to get the PA13 LED blinking.
Please re-download the linked example and switch to the octopus_minimal environment, then flash that via DFU.
If that still does not work, there might a be a problem with the DFU upload. Try building the project normally with PlatformIO, then feed the .pio\build\octopus_minimal\firmware.bin file into STM32CubeProgrammer and tell it to flash it to the standard 0x8000000 address in flash via DFU.
And if that still does not work, the only thing that can help is attaching a SWD debugger to see where exactly the microcontroller is struck. Debugging should work out-of-the-box with that board definition.