Elements Organizer 2019 Problem

The photos shown in your screenshot are all missing files.  (Note the question mark icon in the top left of each thumbnail.)  Without knowing more information about your workflow and setup, it is impossible for us to tell you how they got there.  (But the Organizer did not create them.)  You can safely select any of those thumbnails and delete them from your catalog and they won't show up again.

I note from your folder panel, that you have a number of folders with unusual names.  My suspicion is that when you imported files into your catalog, you used the bulk import method and any photos in these folders were somehow imported into your catalog.  These folders could, for example, be from your email and have been downloaded by you to your computer where they are stored in unique named folders that are not normally searched for photos.

In any event, it would help us (and you) figure out where those folders are actually located, if you use the Tree View of the folders rather than the List View.   If you click on the hamburger icon next to the My Folders heading, you will be offered a choice to switch to View as Tree.

Oh - I've just noticed that you are on a Mac (about which I know almost nothing).  If you have been using a Mac OS application to store your photos or backups of your photos, this could be another cause of what you are seeing.