Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32n6/STM32N655/MCE1/MCE_CC1KEYR3#0x0
MCE cipher context 1 key register 3
cipher key, bits [127:96]
https://github.com/modm-io/cmsis-svd-stm32