In reply to Joseph Dickson.

The "Classic Editor" plugin, by Andrew Ozz, won't disable the nag screen on its own, and doesn't completely disable Gutenberg without changing settings.

"Classic Editor Addon" is a second plugin that fixes both of these behaviors in "Classic Editor". If you install both plugins, Gutenberg will be completely disabled, and you will not see a nag screen.

The only reason "Classic Editor Addon" doesn't just do the whole thing itself is that "Classic Editor" is the official path to disable Gutenberg, and its number of active installs is being used to measure the success of the Gutenberg plugin.

Therefore, if you expect trouble with Gutenberg, it is important to use "Classic Editor", despite its flaws, to let the core team know how many people are having issues with this release.