Hi, sorry for misleading you.
The previous method using flash.sh only supports eMMC/SD, which is not present on Orin NX.
Please use the new tool as specified here:
To back up and restore a Jetson device
Also you need to replace all mmcblk0 with nvme0n1 in nvbackup_partitions.sh and nvrestore_partitions.sh under
Linux_for_Tegra/tools/backup_restore/
for the script to work with NVMe drives.
Check this thread for more detail.