catalog not recognized

Check that Lightroom Classic still has 'Full disk Access' permissions. Maybe this got reset during an update. 

See Quick Tips: How to give Full Disk Access to Lightroom Classic on macOS

I keep my Lightroom Classic catalog on the desktop of my Macbook Pro. where it is updated on a regular basis. After several years of working like this I received a message upon opening LR which said "catalog not found" or something similar to that. When I click on "Open Catalog" and navigate to my desktop the catalog icons are grayed out and not accessible. Any ideas to help me?

By @jonathanr2954463

Sound to me like the folder where the catalog is located has been (accidentally?) moved, deleted or renamed. Or perhaps the actual catalog file(s) have been (accidentally?) moved, deleted or renamed. Or both.

Please use you operating system's search feature to search all folders on all disks for files whose name ends with .LRCAT, might be lower case, those are your catalog files. When you find the one you want, double-click on it.

And ... I hate to have to ask ... but you do have backups of your catalog file, don't you?

What do you mean with “not accessible”?

Are there any messages when you try to open the catalog from within LrC or when you try to open it by double click?

Any changes to your system lately?

Can you share a screen capture of the folder showing the catalog files, and/or the messages appearing.