Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32h5/STM32H523/RAMCFG/RAMCFG_M3ECCKEYR#0x0
RAMCFG memory 3 ECC key register
ECC write protection key
https://github.com/modm-io/cmsis-svd-stm32