Since there is not yet any account to log in to, this is working as expected. Headless should work via the serial console. When you say headless, did you mean you tried serial console?
Normally you must complete first boot account creation and set up either with a local keyboard/monitor, or else via serial console. Serial console information is listed here:
https://www.jetsonhacks.com/2019/04/19/jetson-nano-serial-console/
If you have no way to complete this, then you can use a script to set up the flash software to pre-create the login details. See:
https://forums.developer.nvidia.com/t/jetson-nano-all-usb-ports-suddenly-stopped-working/75784/37