After installing your OS (Manjaro in my case) and configuring it to your likings, which directories do you backup? (or reverse-question, which directories do you not backup?)
Assuming you're using btrfs, just use snapshots. You can also make use of Snapper to automate the whole thing, including setting up hooks for pacman so that it automatically takes a snapshot before an update.
And for portability/reproducibility of your OS config, just backup your dotfiles: