WPCode (formerly known as Insert Headers and Footers by WPBeginner) is the most popular code snippets plugin for WordPress used by over 1 million websites.
Demo: https://wpcode.com
Safely keep all your website customizations together in one convenient dashboard.
Demo: https://codesnippets.pro
With Snippets PRO, you can include snippets of text in your content.
Demo: https://regularlabs.com/snippets