Thumbnails only after upgrade to Photoshop Elements 2023 from 2020

I downloaded Photoshop Elements 2023, and selected one of my catalogs, which are on an external drive, to update. The thumbnails display for each album, but there are no individual photos. To find them, the system tries to go through my computer files, not the separate drive. When I try to match them from the drive, I've so far had no luck. I tried importing them from the file, but am told they're already in the catalog. Since this is only one of a number of catalogs I have, I really need to know how to solve this. I use an iMac and Seagate drive.