My original problem was as follows: Lightroom CC on Windows 10 would give me the 'local catalog damaged' prompt when starting the program. Lightroom CC crashes immediatly after clicking 'ok'
Lightroom CC therefore can't connect to the cloud to repair catalog
What fixed it for me:
Going into the Data folder
Deleting 'profiles' folder
Going into the folder with long string of numbers/letters Deleted all 'Managed Catalog' files Deleted 'preview' folder and preview.db
restarting Lightroom CC for Desktop
Lightroom CC regenerated all of the deleted folders and files when started and didn't crash. I have access to all my photos including the ones which were uploaded via my iPhone. There appears to be no damage at all to any of my images (which makes sense because of the catalog being in the cloud)
I write this all down bc I was stuck without Lightroom CC since January 2021 and could not find anyone with a solution that worked for my specific issue. I hope this helps.
It wasn't clear in adobe's resolution to the error that the MCAT file needed to be deleted.
I had the same issue with MAC OS and this article resolved the issue. Thanks @ariss50924415
I saved the MCAT file, preview folder, and preview db file to an external hard drive just to be safe, then deleted the MCAT file from the MAC OS. I retarted Lightroom and it began syncing all photos, edits, etc.