Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32u5/STM32U535/FDCAN1_RAM/FDCAN_TXBC#0x0
FDCAN Tx buffer configuration register
Tx FIFO/Queue Mode
https://github.com/modm-io/cmsis-svd-stm32