Photoshop Elements 2018

You can't "deactivate" the organizer but you can ignore it. (You can also use it selectively for smaller catalogs; it can be installed as well as Photoshop CC and Lighroom for use by another user for instance.)

Open the organizer menu Edit >> Preferences and uncheck any automatic task (in Files and Autoanalysis...)

In the File menu, erase anything in the 'Watched folders" dialog.

When working in the editor, be sure not to tick the checkbox to include in the organizer or as a version set when saving files.

You can always create a new empty catalog from the catalog manager. It's necessary for the organizer to open; when you are in the empty catalog, you can delete any other catalog from the catalog manager.