The instructions you referenced make a copy (of the relevant parts) of the files on the root partition.
To make a copy of an OS you ALSO need to copy the files on the boot partition AND the partition table (or be able to re-construct one with the right settings).
Your earlier attempt failed because you only restored part of the image.
In order to restore to the same SD Card it MUST already have the same kernel/firmware - OR you need to have made a copy of the boot files. My restorations have usually been to recover from operator error.
If copying to a new SD Card it needs to be partitioned and formatted FIRST any you need to modify PARTUUID entries in BOTH /etc/fstab and /boot/cmdline.txt to match your SD Card.
The above are not difficult, but there are quite a few steps.
I regularly create SD Card images (to use as security backup) particularly before major updates - although I rarely use the images. See Clone Raspberry Pi SDCard to file on Mac OS X? (this is
macOS specific - there are plenty of examples for other OS) On the few occasions when I have to restore this is simple - and I can go back to historic backups if necessary.
I also use
rsync to backup files to disk See Can a Raspberry Pi be used to create a backup of itself? These are mainly used to restore specific files. I also use
rsync to synchronise SD Card images.
PS SD Cards rarely break. I have only had 3 or 4 corrupted cards with 16 cards and too many Pi over more than 6 years and only a single failure.