The pad for SPI-Flash on the WeAct-f411ce does not come pre-populated. The user has to manually solder a SPI-flash chip on the board, so specifying a size here makes no sense. Instead, rely on automatic detection of the flash size at run-time.
The WeAct-F411CE is a blackpill-like board with a STM32F411CE. It can be flashed using the vendor-provided bootloader.