Arduino for STM32

I already uploaded the ‘old’ STM32duino bootloader with my usb to uart adapter.
I don’t understand why would I always have to use the adapter to load programs, because if you search “STM32 arduino” on the internet, people just load the STM32duino bootloader on their blue pill which has the same ...

Hello,
I'm trying to load the blink sketch on one of my first STM32 board that I designed. (It's the STM32F103C8T6)
It is detected by my Mac when I plug it, but then, when I simply try to load the Blink sketch, it outputs me this error :
dfu-util: Invalid DFU suffix signature
dfu-util 0.8
dfu-util ...