I was about to migrate from Lightroom Classic to Lightroom CC. I was backing up the catalogue in Lightroom Classic before I told Lightroom CC to import the catalogue, when I got a message pop up that the catalog was damaged and needed repairing, which was followed by this message:
'Unfortunately the catalog named 'Lightroom Catalog cannot be repaired'
It gave me the option to contact Adobe support (which led me here), Show in finder, Quit or Choose a Different Catalog. All of the other catalogues look like they are ages old, even though I've had it set to back up once a week forever.
This is a user-to-user forum, we are not Adobe support.You need to find your recent bakcups. Use your operating search feature to search ALL hard disks for files whose name ends with .LRCAT or .LRCAT.zip
I had a problem opening my catalog. I created a new one and then imported from the old catalog to the new one. This would recreate the old catalog structure and then you can import the actual images. This worked for me, although the images were rotated and I had to rotate to correct, they had my changes intact. Hope this helps