If you mean the option under System > Backup/Restore, yes – but since it only creates a very small file (~6kB), I assume it only contains certain configurations. I would like a backup that when restored puts the system in exactly the same state as at the time of backup, including all extra packages, scripts etc.
Since also doing a firmware upgrade erases packages I've always used the Image Builder https://openwrt.org/docs/guide-user/additional-software/imagebuilder to make a full firmware image with all packages included, and at that point the only thing I need to backup/restore is the config files, which are handled by default Luci/OpenWrt backup system.
Yes DO NOT directly copy and restore mtd partitions on a device with NAND flash, that will brick it. On most routers with NOR flash you can make an image to clone or restore the installation with a copy of the "firmware" partition (which is an alias for kernel + rootfs + rootfs_data). Install this file with sysupgrade -n.
OpenWrt does not alter the bootloader, factory, or ART partitions so there is no need to restore those. Writing to these partitions can result in loss of unit-specific factory data that is difficult or impossible to recover.
Thanks to everyone. I have now found and read a number of instructive pieces that I recommend to anyone with the same question:
– and particularly
Between all of these, I think I'll figure out what works for me. I have already installed opkg extras and ensured that I extended the list of directories and files to be backed up; this made me understand why my backup file (with default settings) was so small.