Erin McIntyre

This plugin searches links on your site for the domain that you specify in the settings, adds your affiliate ID, and makes those links open in a new tab when clicked.
The plugin produces XHTML Strict compliant code and is search engine optimized (SEO). 
This is done using JavaScript’s <code>window.open()</code>-function. It adds only a few lines of vanilla JavaScript to the page, and does not require any external libraries like jQuery.
Most other plugins perform a hack by altering the <code>target</code> parameter (i.e. <code><a href="http://somewhere.example" target="_blank"></code>). That method is not XHTML Strict compliant.
This plugin handles the links client-side, which lets search engines follow the links properly. Also, if a browser does not support JavaScript, the plugin is simply inactive, and does not result in any errors.
Credits 
Inspired by the <a href="https://wordpress.org/plugins/open-external-links-in-a-new-window/" rel="ugc">External Links in New Window / New Tab</a> plugin.
Known bugs 
The plugin conflicts with other plugins that change the links’ `onClick´ attribute.

Affiliatize Me

Cristi Tamas

Cristian Outbound Manager is a lightweight and reliable plugin that automatically handles all outbound/external links on your WordPress site. Improve SEO, security and user experience with zero effort.
Once activated, the plugin scans your post content and applies the attributes you choose:
<ul>
<li>Open external links in a new tab (<code>target="_blank"</code>)</li>
<li>Add <code>rel="nofollow"</code></li>
<li>Add <code>rel="noopener noreferrer"</code> for security</li>
<li>Exclude specific domains from being modified</li>
</ul>
Perfect for blogs, business sites, affiliate sites, WooCommerce stores and any website that uses outbound links.
This plugin is fully compatible with PHP 7.4 – 8.4.
<h3>Features</h3>
<ul>
<li>Automatically detect outbound/external links</li>
<li>Add <code>target="_blank"</code> to open links in a new tab</li>
<li>Add <code>rel="nofollow"</code> to external links</li>
<li>Add <code>rel="noopener noreferrer"</code> for security</li>
<li>Exclude domains (one per line)</li>
<li>Lightweight and fast — no impact on performance</li>
<li>Works with Gutenberg, Classic Editor, page builders and custom post types</li>
</ul>

Cristian Outbound Manager

Manage outbound links automatically: open in new tab, add nofollow, noopener, and exclude domains.

Affiliatize Me vs Cristian Outbound Manager