Which exact version of Lightroom are you using? There are two main versions. One is called just Lightroom and stores all originals in the cloud. The second is Lightroom Classic and is much more fully featured but stores all images locally. If you are in the cloud version, backup is not simple. You either export as original, which will put all the raw files with xmp sidecar files in the location you choose. The xmp sidecar files are actually included inside dng, tiff, or jpeg files if those were your originals and they contain all the editing instructions needed by Lightroom or camera raw in Photoshop to recreate your exact edits but when you open the raw file in any non-Adobe program you won't see the edits. This is how raw files work.
If you use Classic, simply set your local storage folder to backup using time machine or another dedicated backup solution. You can also export manually or using a publish service all highly rated images to a location on your harddisk (e.g. your dropbox folder to back them up to the cloud!) and generate backups of just your important images.