We found an issue on Jetson Nano that it was not able to load kernel, kernel-dtb and initrd from USB or NVME. The fix for this issue is in a python script that we have posted now here: https://developer.nvidia.com/l4t-payload-updater-t210
We are updating the documentation as well but please follow below steps for flashing USB or NVME for Jetson Nano:
Step 1: Prepare rootfs by untaring the BSP, untaring the rootfs and running apply_binaries.sh as mentioned in section “Setting up your root file system” in the developer guide here: https://docs.nvidia.com/jetson/l4t/index.html#page/Tegra%20Linux%20Driver%20Package%20Development%20Guide/rootfs_custom.html#wwpID0E0NB0HA
Step 2: Copy the python script which has the fix from https://developer.nvidia.com/l4t-payload-updater-t210 to rootfs/usr/sbin/l4t_payload_updater_t210
sudo cp <l4t_payload_updater_t210.py> rootfs/usr/sbin/l4t_payload_updater_t210
sudo chmod a+x rootfs/usr/sbin/l4t_payload_updater_t210
Step 3: Follow the instuctions for flashing to USB or NVMe from https://docs.nvidia.com/jetson/l4t/index.html#page/Tegra%20Linux%20Driver%20Package%20Development%20Guide/flashing.html#wwpID0E02L0HA
Please remember to remove the microSD card from Jetson Nano or else Jetson Nano will try to boot from microSD card.
Also, plase remember that to load from USB, one need to have an update QSPi, so just bootup with JetPack 4.5 SD card image once which will update the QSPi and then you are good to go from then on.