** This is a mistake; I didn't know there was already an existing package in the Zephyr source tree called blackpill_f411ce that supports BluePill-Like boards. **
west flash -b blackpill_f411ce
Tested with Zephyr 2.4.99.
oldrev/stm32-mini-f411-blinky-zephyr
A Zephyr-RTOS Blinky Demo for BluePill-Like STM32F411CEU6 Development Board
C