Uploading code on to STM32 Bluepill Arduino core is through serial bootloader at USART1 or through ST LINK at SWID.
USB also can be used to upload code.
This video is on how to implement USB BOOTLOADER SUPPORT toSTM32 BLUEPILL
Flasher tool download :
https://www.st.com/en/development-too...
Driver support :
https://github.com/rogerclarkmelbourn...
.bin file for PC13 builtin LED board :
https://github.com/rogerclarkmelbourn...