How do I revert to previous Lightroom Version?

Did the upgrade select the correct catalog? You might want to use Finder and see what catalogs you have. Sometimes if the preference file is corrupted, an upgrade selects the wrong catalog or even no catalog at all (new catalog)

I've moved your thread from the Lightroom Ecosystem to Lightroom Classic forum.

It's possible to roll back to an earlier version: https://www.lightroomqueen.com/roll-back-update-previous/ 

And then you'd need to open your previous catalog, not the upgraded one.

But before you do that, perhaps we can help you fix the problem you're having? Start by showing us a screenshot of Lightroom's Folders panel, telling us where the catalog's stored, and which macOS version number you're using please?

I am replying to follow. I am having sognificant issues, as well.