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:

rsync -avh --exclude={'.local/share/Trash','.Trash-1000','.cache','/[^.]*'} ~/ /mnt/backupfolder/ --delete

and package list.

And for your personal documents, just use your favorite own/cloud service provider’s tool.

/etc and ~/.config in priority