Hi mhnrshd93,
What’s you Jetpack version in use?
Please refer to the following thread about the UART mapping for Orin NX.
OrinNX : How to check UART is working? - #3 by KevinFFF
UART0 should be connected from M.2 Key E, have you connect them on the custom board to your UART device already?
Please just enable it from the dtb in use.