The answer can be found in datasheet page 10:
FS32R274KBK2MMM: configuration B = CSE yes
FS32R274KCK2MMM: configuration C = CSE no
Two parts are pin-compatible.
CSE is short for Cryptographic Security Engine which aims at enabling advanced security management, such as security boot. For more infomation please refer to reference manual, or directly reach me out: email@example.com
Hope it can help.