The WordPress team decided that this plugin is not going to deactivate the new Gutenberg widget area. Instead, a new Classic Editor plugin is launched: https://wordpress.org/plugins/classic-widgets/
Hi @melissaknight, as @davelo mentions there is a Classic Widgets plugin that lets you switch to the old widgets editing screens. It’s super easy to use: just install and enable it. There are no settings.
Note that it is a “site-wide” plugin, other users (if any) will not be able to switch back and forth.