Nhat Huynh Van

<blockquote>
It’s hard to change if you love something!
</blockquote>
I’ve been using the original/classic editor for over 10 years now and the experience has always been 100% smooth and the original Visual Editor was awesome. 
I like to keep that to myself and I’m sure there are some people like me who like the classic, easy to use and simple thing.
This plugin disables the new Gutenberg Editor (Block Editor) and replaces it with the Classic Editor. 
The Disable Gutenberg plugin restores the classic (original) WordPress editor and the “Edit Post” screen.
Features
<ul>
<li>Classic Editor</li>
<li>Disable Block Widgets and restore Classic Widgets</li>
<li>Enable/disable frontend Gutenberg stylesheet</li>
</ul>
<blockquote>
Works same as Classic Editor plugin, but lightweight, simple and super fast
</blockquote>
Easy to Use
<ul>
<li>Super simple</li>
<li>Clean, secure code</li>
<li>Built with the WordPress API</li>
<li>Lightweight, fast and flexible</li>
<li>Works great with other WordPress plugins</li>
<li>Focused on flexibility, performance, and security</li>
</ul>

Relive Classic

Plugin Relive Classic is help you use editor, widgets in classic style and disable Gutenberg.

Farid Mia

This plugin disables the Gutenberg Editor and Gutenberg widget block. 
You can totally disable Gutenberg. After activating this plugin, the classic editor and widget will be enabled automatically.

Disable Classic Editor and Widget

This plugin disables the Gutenberg Editor and Gutenberg widget block.

Relive Classic vs Disable Classic Editor and Widget