There is an open-source firmware that is better in many ways. https://github.com/blacksphere/blackmagic https://github.com/blacksphere/blackmagic You can even

There is an open-source firmware that is better in many ways. https://github.com/blacksphere/blackmagic https://github.com/blacksphere/blackmagic You can even debug on a $2 "blue pill" or wirelessly on a $1 esp8266 board. It has certainly not hindered STM32 popularity.