this is less helpful than you might think.
basically all packages, which get installed during system installation are marked as “explicitly installed”. you can get a list of all of them with “pacman -Qqe”.
such a list would really be useful, if you want to backup your current system (which requires to backup your home folder and many files in /etc/, too) (attention: such a list also contains AUR packages).
such a backup utility would need to read the list again and install all packages in it (if those packages still exist in system repository or AUR). before doing that, a check for existing AUR helpers is required in order to install AUR packages (if such an AUR helper is not found, a good one should be installed).
in addition, you should not keep installing the same packages on your system for years, because packages might reach their end of life (and/or have security vulnerabilities) or there are better packages. dependencies of DEs or other system packages can change. you would need to maintain such a list of packages similar to maintaining a manjaro spin.
in summary, writing such a backup utility is possible (within the roams of manjaro - do not expect arch linux / AUR maintainers to accept such an utility!), but it is more work than you might think. i think it is easier to keep a backup of your home directory and reinstall your system from an ISO.