João Carmo Pereira

This plugin will add a new copy to clipboard functionality to Gutenberg Code Block. 
It will add a copy button at the top right corner of the block. After clicked, it will select the text, copy to clipboard, and after copy it will deselect the copied text. No markup here.
This plugin makes use of two javascript libraries: 
Clipboard.js and Prism.js

Carmo Copy to Clipboard

This plugin will add a new copy to clipboard functionality to Gutenberg Code Block.

hypercoder

CodeBlock is a free WordPress plugin that enables visitors to copy programming code with a single click. It features:
<ul>
<li>A simple lightweight plugin in with no dependencies; the whole package consist of a PHP, a JavaScript and a CSS file (1.92KB)</li>
<li>Makes use of short-codes</li>
<li>Works with stylized code. That is, it only copies the code not the underlying HTML elements</li>
<li>Spam free. It will never bag (ehm, bug) you for ratings, permissions…etc.</li>
</ul>

HyperCoder CodeBlock

CodeBlock is a free WordPress plugin that enables visitors to copy code blocks with a single click.

Carmo Copy to Clipboard vs HyperCoder CodeBlock