Up to date with Apple iMac and Adobe (Photo)..... I decided to do a tidy up of photo files by copying them to WDMyCloud external backup hard drive. Then I explored how they would be imported back to Lightroom should I decide to delete all photos from the internal hard drive. Luckily I didn't delete! Looked at import, I find that Lightroom does recognise this drive, but cannot enter it via Lightroom. HELP!
Went back to "Finder" and it does open it...Just checking.
Oops.. It is Lightroom Classic.
As I am not a MAC person, I don't know the answer to your question.
However, the idea of deleting photos from Lightroom Classic and then importing photos back into Lightroom Classic is something you should never actually perform. Get this idea out of your brain. Re-importing photos is almost never a good thing to do. Deleting followed by importing is simply not a good idea, it is a terrible horrible bad bad bad idea.
To move the photos such that Lightroom Classic still recognized their location and is able to use them, there is NO IMPORTING. Follow the instructions in "Part 2 - Updating Folder Location" in this document: http://www.computer-darkroom.com/lr2_find_folder/find-folder.htm
REMEMBER: NO IMPORTING to do this
Another comment: you say the WDMyCloud is a backup drive. But if you delete the originals from the internal hard drive ... you have NO backups (despite you using the word "backup" to describe the drive). This is not a good situation.
We my cloud is just a very simple (and not very reliable but I digress) NAS server. You can definitely have images on it and access them through Lightroom Classic. When you copied them over and tried to import them, Classic recognized it already had these images in their original location and refused to import them. This is in general NOT how you move images or backup images with Classic. You can offload images to a network drive such as this thing if you want using the process described here: https://www.lightroomqueen.com/move-photos-another-hard-drive-leaving-catalog/
the process is identical for network drives. If you use any other method, you WILL lose your edits as already mentioned. Lightroom Classic is just a catalog that points to files on your hard drive, external or network drives. If you move files outside of Classic it loses the connection and you will have to relink the images. Make sure you have another backup before you do any of this. As also said, if your images are not in two places simultaneously, you do NOT have a backup.
How you guys have helped!!!
After all of your help, I went on to "Tim Grey" who has a YouTube channel with Adobe and he covers it in real depth.
Again a huge thanks.
As a "by the way", I have been well warned now to move WITHIN Lightroom only from now on and have managed, with your help, to get the Back-up (and the back-up of the back-up) onto extrernal drives and only the cat.. remains on the desk top.
Was a worry.