Hi,
I am not sure what should be the voltage level, but checking the Jetson Nano Pinmux document (NV_Jetson_Nano_Module_Pinmux_Config_Template.xlsm), it indicates for most of the GPIOs: IO Block Voltage: 1.8V
Have you seen this forum: Jetson Nano Dev Kit GPIO Pin giving 1.8V output instead of 3.3V, maybe it can help you.