Hi phamxuanvi93,
Please help to share the result of the following command for Jetpack version in use
$cat /etc/nv_tegra_release
Your result seems unexpected. Do you save the pinmux configuration in Jetson-IO and reboot the board to apply?
Could you help to refer the following thread step-by-step for SPI loopback test?
Jetson Nano SPI Bus Not Working - #10 by KevinFFF