I don't know how to make this simple!

Your photos were/are never "IN" Lightroom. Lightroom only records where they are and changes you make to them. The photo files remain untouched.

Your photos are where you put them in the computer file structure. You may have used Lightroom to put them there. Or you may have put them there by other means and then "Imported" them to Lightroom. Importing does not really bring photos inside of Lightroom, it only records where they are and makes previews. Adobe should rename "Import" to "Record Location".

If due to computer or drive failure, the files disappear, Lightroom will still think it knows where they were. So, if you replace them in a restore sequence to where they were, Lightroom will "see" them. The backup/restore sequence is done outside of Lightroom and is a critical process. If the files get renamed or put elsewhere, Lightroom won't know where to look.

If it were me, I would restore the photo files to my drive from my backup in a way to ensure they were EXACTLY where they were. That should be done in a Restore process. Lightroom can't do it. The drive name has to be the same or changed to match what it was. Once that is done, I would find a Lightroom catalog backup, open it and use it.

If you can't make Lightroom relink with your photo files, you have to start over. Put all your photos where you want, open a NEW catalog in Lightroom and Import everything. The good part is that you still have your photos. The bad part is that all the Lightroom editing you've done will be lost.