A Jetson in recovery mode should show up with lsusb, and for the NX, this means recovery mode must be running and the micro-B USB connector.
A fully booted Jetson usually has some device emulations going on over the micro-B USB as well, but that depends on circumstances. When a device flashes in recovery mode there is no dependency on anything being installed, but when flash completes and reboots, then it depends on what is currently running.
If you are flashing, then are you sure you are using recovery mode?
Assuming the cable is working, and that a VM is not being used, then this indicates a hardware failure. A Jetson in recovery mode should always show up under lsusb, and very little software is involved…which means hardware error (if you are absolutely certain boot was with the recovery mode jumper, then the jumper removed after power up).