Can't locate photos after moving catalogue to Hard Drive

It's important to understand the difference between the Lightroom catalog and your actual photos. The photos are not in the catalog but are kept separately in a place you told Lightroom to store them. 

If the photos are actually in the Lightroom folder that you moved, you'll need to connect the folders within the Lightroom app itself (Folders panel) to the new location. When you "Find Missing Photos," you need to point Lightroom to the new location. This is an easy process if you have one top level folder on the hard drive containing all the sub folders with your photos. Just reconnect the top level folder and all should be well. If you have many top level folders, you'll have to reconnect every one of them. 

If the solution from @AxelMatt doesn't help, you need to explain this part in much more detail.

Even when I attempt to "find missing photos," I cannot link any catalogue to the backups,

What backups are you referring to? What did you do, step-by-step, in detail? What happened? Describe in detail.

Please take a look here:

https://community.adobe.com/t5/lightroom-classic-discussions/quick-tips-how-to-give-full-disk-access-to-lightroom-classic-on-macos/td-p/12913413

and see if it helps.