Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/STMicroelectronics/STM32H7x5_CM7/FDCAN1/FDCAN_TXEFS#0x0
FDCAN Tx Event FIFO Status Register
Event FIFO Fill Level
Event FIFO Get Index.
Event FIFO Full.
Tx Event FIFO Element Lost.
https://github.com/cmsis-svd/cmsis-svd-data