I've suddenly lost all link to my only catalog, with a message "No photos in selected Folder. Subfolders not shown." How do I utilize the saved backup, and is that the correct "fix"? Thanks.
Check your recent catalog list just in case you created a new catalog by mistake.
To use a backup catalog:
Navigate to your folder containing the backups of your catalog.
Go into the folder for the most recent catalog backup.
Copy the LRCAT file to a new location, near the old catalog would be good but do not overwrite the old catalog.
In LR, open the copy of the backup by going to menu:/file/open-catalog/
and navigating to the copy you just made.
Do not directly open the catalog in the backup folder.