During flash the Jetson has to be connected and in recovery mode. When the unit has flash complete it reboots and install of some options are then added over
ssh to a fully booted Jetson, but this requires having completed the first login setup for an account. If the virtual wired ethernet over USB is used for
ssh networking, then USB has to remain connected, but it is for networking instead of being for recovery mode. If you’ve instead named an IP address from the ethernet port, then you could technically remove the USB cable at that point (but it wouldn’t be necessary).
So you should see the monitor have activity and offer a first boot setup all by itself. If not, then you could cycle power to get it to reboot, but only do so if the flash (but not
ssh optional component install stage) is complete.
FYI, you can (and might prefer due to less complication) uncheck all steps except flash, and complete flash. Or you can uncheck flash if flash completed once, and just check steps to install optional content, e.g., CUDA.
Once actual flash is done and the first boot setup of account is done you can use the Nano almost like a desktop PC.