Buster backup the image
From embeddedTS Manuals
To create backups / restore images, it is recommended to first boot to USB. A disk should not be backed up or written while it is used to boot.
If your image is a single partition it can be backed up as a tar file. This allows the media to easily expand to any disk size.
Create a backup tar
mkdir /mnt/emmc
mount /dev/mmcblk0p1 /mnt/emmc/
tar -cJf /root/backup-of-image.tar.xz -C /mnt/emmc/
umount /mnt/emmc/
Write a tar image to the eMMC
sgdisk --zap-all /dev/mmcblk0
sgdisk -n 0:0:0 -t 0:8300 /dev/mmcblk0
mkfs.ext4 /dev/mmcblk0p1
mkdir /mnt/emmc
mount /dev/mmcblk0p1 /mnt/emmc/
tar -xf /root/backup-of-image.tar.xz -C /mnt/emmc/
umount /mnt/emmc/