P: Unexpected error opening catalog on macOS

Can I manually move the location of the new backup to the original backup folder and then direct any future backups to the original folder?

When the backup dialog next pops up, you can set the location of your choice in there.

Not sure, maybe the Adobe employees or Victoria knows, but it’s not normal. Maybe if you “adopted” a backup as your new catalog it creates a new set of backups for that?

Thanks for your help! One thing I notice now is I now have 2 separate Backups folders. One with my old backups, and a new one where any future backups will go it appears. Is this expected?

Excellent news. We may never get to the bottom of what corrupted the catalog (but it could have been the Dropbox sync), but I'm really pleased we got you back up and running!

Update: details on how this problem was resolved here

Yes that's sufficient. You can find the Adobe support number on their site? PS-don't upgrade the OS to 10.14.6 (it breaks the panorama function in LR). Also, have you tried opening one of the Backups (by double-clicking on one)? The Backup folder is in the same folder as your Lightroom catalog, generally in Pictures? Choose the most recent, if that's hosed then try other recent ones.

Carlos, I am back. I downloaded and ran Onyx without success. Below is an image of what I cleared using it. Would this have been sufficient?

Alternatively, is there an Adobe support person I can communicate with? This is a massive roadblock in my workflow. 

Can you confirm this is the correct Onyx software?
https://www.titanium-software.fr/en/onyx.html

You could delete Launch Services (which just resets which app opens which files by default, but if you’ve ever changed that, with a right-click “Open with...”, you’d have to reset it (so unless there’s an issue with that I just leave it alone). Use your knowledge of internet browsing to save your browser history, form values, cookies, etc. if you don’t know what something means, like “cookies”, then do a web search for it. Generally it’s mostly the internet cache that you’re trying to delete in the Internet area. If you don’t understand something don’t delete it! Mostly you’re trying to get rid of caches, application states and saved versions.