Steven G. answered 09/06/24
Photographer and Instructor of Adobe Photoshop and Lightroom
Lightroom is still looking for the images on the original disk because they were moved using computer's operating system. If they had been moved using the Lightroom processes they wouldn't be "lost."
Find the highest level folder (the one that contains all the other folders) and RIGHT CLICK on it. You will see a menu item "Find Missing Folder". Click that and navigate to the new disk with the high level folder. Choose that one and press Enter/Return.
Those images will now be available since the Lightroom database (the catalog) "knows" where they are!
Note: if there are a lot of images is can take a few minutes for the updated location to be usable.