I2C works okay for both STM32F103C8T6 and CS32F103C8T6.
PlatformIO made the Blue Pill board stuck at DFU mode. What now?
I finally programmed the Blue Pill board using DFU protocol from PlatformIO.
Yeah, finally managed to upload program directly from the micro USB connector.
What are the odds that all three Blue Pill boards didn’t work?!