Step 1
Open the returned catalog
Question marks or grey previews usually mean Lightroom cannot see your original file path.
Step 2
Open the Folders panel
In Library, locate the folder with the missing-file indicator.
Step 3
Choose Find Missing Folder
Right-click and choose Find Missing Folder or Update Folder Location.
Step 4
Point Lightroom to your originals
Choose the local folder containing the RAW/JPG files used by the returned catalog.
Step 5
Confirm relinking
The images should populate normally after the folder is found.
Step 6
Locate individual missing files
Click the missing-file icon, choose Locate and enable Find nearby missing photos when useful.