That's the thing, STM32s are jellybean devices that you can tenth-source from anywhere, including some guy cooking them up in his kitchen in Shenzhen. This thing is an STM32 in name only (SINO? STINO?).

Eh... that really depends on the part. Some common, old parts like STM32F103 are more or less second-sourcable; others like the STM32H7 series aren't.