Note that the module itself tends to have 1.8V levels (not all, so be careful, this is a “general” statement). References to pins on the carrier board usually say 3.3V because of a level converter. For the development kit carrier board J24 can optionally be set to either 1.8V or 3.3V for some of the I/O, with the default position being 3.3V.
UARTs from the carrier tend to all be 3.3V, and although they will probably tolerate 5V I would not expect this to function.
Many USB serial UARTs provide the serial UART pins plus the 5V power made available to USB devices. That 5V is not used since the UART on the Jetson side is already powered. In cases where there is a 5V pin just ignore it…but if it says the I/O level is anything other than 3.3V, then you probably need a different UART.