Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32l5/STM32L552/FDCAN1/FDCAN_TXFQS#0x0
FDCAN Tx FIFO/Queue Status Register
Tx FIFO Free Level
TFGI
Tx FIFO/Queue Put Index
Tx FIFO/Queue Full
https://github.com/modm-io/cmsis-svd-stm32