One can use serial programming, with genuine STM32 MCUs, Single Wire Debug (SWD) via the four-pin break-out header, or the USB port if a suitable bootloader is installed. The schematic for the ...

And just how hard is it going to be to port low-level code from STM32 to RP2040? Raspberry Pi Pico RP2040-based board, hooked up to a Raspberry Pi SBC acting as SWD dongle. Long story short ...