Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/STMicroelectronics/STM32U599/FDCAN1_RAM/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/cmsis-svd/cmsis-svd-data