Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32l5/STM32L552/FLASH/NSSR#0x0
Flash status register
NSEOP
NSOPERR
NSPROGERR
NSWRPERR
NSPGAERR
NSSIZERR
NSPGSERR
OPTWERR
OPTVERR
NSBusy
https://github.com/modm-io/cmsis-svd-stm32