Properly creating a system backup with tar?

Lot of guides focus on how to backup user data, but I'm interested in backing up the current state of my Debian Buster system. Why? Because I've had a few experiences of breaking something or other on my system with an ill-advised install or update, and as a Linux newbie I don't know how to fix it so would like to have a backup of the system that I can just restore.

Does it make sense to use tar for this? I see discussion about directories (and files) that shouldn't be backed-up and restored, but different things in different discussions so my head is kind of spinning. Can anyone suggest a tar command to backup the system in a way that would allow it to be easily restored?