SD Card Image MTD partition 'rootfs_data' not found

I am using a custom build of OpenWRT (23.05) for a custom piece of hardware. We boot OpenWRT off an SD card. Booting works fine and we can interact with the filesystem (read/write). I want to use the firstboot command as part of our reset process but when I call it, I get the following error:

MTD partition 'rootfs_data' not found

We have both ext4 and squashfs selected in Target Images when we build the OpenWRT image:
image

Is it possible to use the firstboot command in our scenario? Based on my googling, here is the output of some reference command that might be useful:

root@SwordfishGateway:~# df -h
Filesystem                Size      Used Available Use% Mounted on
/dev/root               102.3M     44.5M     55.7M  44% /
tmpfs                   121.4M     80.0K    121.3M   0% /tmp
tmpfs                   512.0K         0    512.0K   0% /dev
mount
/dev/root on / type ext4 (rw,noatime)
proc on /proc type proc (rw,nosuid,nodev,noexec,noatime)
sysfs on /sys type sysfs (rw,nosuid,nodev,noexec,noatime)
cgroup2 on /sys/fs/cgroup type cgroup2 (rw,nosuid,nodev,noexec,relatime,nsdelegate)
tmpfs on /tmp type tmpfs (rw,nosuid,nodev,noatime)
tmpfs on /dev type tmpfs (rw,nosuid,noexec,noatime,size=512k,mode=755)
devpts on /dev/pts type devpts (rw,nosuid,noexec,noatime,mode=600,ptmxmode=000)
debugfs on /sys/kernel/debug type debugfs (rw,noatime)
bpffs on /sys/fs/bpf type bpf (rw,nosuid,nodev,noexec,noatime,mode=700)
root@SwordfishGateway:~# cat /proc/mtd
dev:    size   erasesize  name

Thank you for any help you can provide! I'm pretty new to all this so please let me know if this is the wrong approach to reset our device.

Have you tried that with an image which would use squashfs instead of ext4? My understanding is that you can't use firstboot with ext4, due to the nature of the ext4-based images.

Thanks for your response! Is there a way to put a squashfs image on an SD card? The output of my build process has squashfs.ubi file but no sdcard image (other than the ext4 one I used above). Is that what I would use to flash the SD card if that is possible?