Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32h5/STM32H523/IWDG/IWDG_PR#0x0
PR=B_0x0
IWDG prescaler register
Prescaler divider
0 (B_0x0): divider / 4
1 (B_0x1): divider / 8
2 (B_0x2): divider / 16
3 (B_0x3): divider / 32
4 (B_0x4): divider / 64
5 (B_0x5): divider / 128
6 (B_0x6): divider / 256
7 (B_0x7): divider / 512
https://github.com/modm-io/cmsis-svd-stm32