Could you help to refer to the following thread to do loopback test?
Jetson Nano SPI Bus Not Working - #10 by KevinFFF
Does your custom board design refer to p3509 instead of Orin Nano devkit for Orin NX module?
Could you help to provide the following device tree?
- Linux_for_Tegra/bootloader/t186ref/BCT/tegra234-mb1-bct-pinmux-p3767-hdmi-a03.dtsi
- Linux_for_Tegra/bootloader/tegra234-mb1-bct-gpio-p3767-hdmi-a03.dtsi