Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32n6/STM32N645/FDCAN1/FDCAN_TXFQS#0x0
FDCAN Tx FIFO/queue status register
Tx FIFO free level
Tx FIFO get index.
Tx FIFO/queue put index
Tx FIFO/queue full
https://github.com/modm-io/cmsis-svd-stm32