Hi 1113088687,
Please update to latest JP5.1.1(R35.3.1).
You could refer to the following thread for UART usage on AGX Orin.
Unable to correspond to "func" and "uart_tx" - #3 by KevinFFF
UART3 seems be used as the debug console.
You could use UART2 as normal serial port for your custom usage through /dev/ttyTHS4
.