I am using an Imac iMac (21.5-inch, Late 2013) MacOs Catalina version 10.15.7 (19H1217) and Lightroom Classic 10.3.
When I try to import images into my normal catalog the progress bar in the upper left hand corner starts but stops and lightroom hangs. When importing I select copy and I can see in Finder that Lightroom has copied the images to the destination folder before hanging. I have optimised the catalog.
Importing into another catalog works fine.
I have reboothed the computer and reinstalled Lightroom and verified that Lihtroom has full disk access.