I’ve so far flashed a microSD card twice with Balena Etcher saying it succeeded both times, followed all the directions on this page https://developer.nvidia.com/embedded/learn/get-started-jetson-nano-2gb-devkit#setup-display, but I’m getting no response whatsoever from the board – no green LED that I can see, and no boot.
Did you jumper J48? A missing green light indicates “no power”.