Photos are no longer referenced and Folders display is empty.

Hello, I am using Lightroom Classic on MacOS. I added some photos to my catalog and at some point it stopped building previews. I tried forcing it, etc. but nothing.
Now I noticed that the Folders panel on the left is empty. When I try to add a folder where referenced photos are, nothing happens. When I right click on a photo, the option to Show in Finder is greyed out.
What can I do here? Really frustrated!
Thanks!
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