Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32wl3/STM32WL33/RNG/RNGPCellID1#0x0
RNGPCellID1 register
These bits are read back as 0xF0
https://github.com/modm-io/cmsis-svd-stm32