Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/STMicroelectronics/STM32H7x5_CM7/FDCAN1/FDCAN_RXF0C#0x0
FDCAN Rx FIFO 0 Configuration Register
Rx FIFO 0 Start Address
Rx FIFO 0 Size
FIFO 0 Watermark
https://github.com/cmsis-svd/cmsis-svd-data