Some time ago I did design this Arduino Mega replacement board for Speeduino ECU that uses STM32F407 processor. With this processor board you can have all the modern features that Speeduino offers, on your old speeduino ECU just by swapping out the processor card.
My GitHub page for this board: https://github.com/pazi88/STM32_mega
PCBWay to order boards: https://www.pcbway.com/
This board at PCBWay: https://www.pcbway.com/project/shareproject/STM32_F407_Processor_Board_for_Speeduino_4fc7d500.html
STM32Cube Programmer: https://www.st.com/en/development-tools/stm32cubeprog.html
My GitHub page for the BMW PnP boards: https://github.com/pazi88/Speeduino-M5x-PCBs
Speeduino Page: https://speeduino.com/home/