Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32n6/STM32N645/FDCAN1/FDCAN_RXF0A#0x0
FDCAN Rx FIFO 0 acknowledge register
Rx FIFO 0 acknowledge index
https://github.com/modm-io/cmsis-svd-stm32