Derrick Hammer

This plugin will automatically have the CriticalCSS.com web service get the needed above the fold CSS for every page on your site to help improve your user experience and site speed. This is commonly required by google pagespeed as one of the last steps to do.
This plugin alone will not improve site performance. You need a minify and/or caching plugin as well.
This plugin does not handle any minification or re-ordering of assets. I recommend using <a href="https://wp-rocket.me/" rel="nofollow ugc">WP Rocket</a> with my <a href="https://wordpress.org/plugins/rocket-footer-js/">WP Rocket Footer JS</a>, <a href="https://wordpress.org/plugins/rocket-async-css/">WP Rocket ASYNC CSS</a>, and the plugin <a href="https://wordpress.org/plugins/the-preloader/">Preloader</a>
If you are looking for a professional team to get your WordPress site to run faster, check us out for our speed optimization services at <a href="https://rankgrowdigital.com/" rel="nofollow ugc">Rank Grow Digital</a>

WP Critical CSS

Triggers a fatal PHP error:

Fatal error: Uncaught ArgumentCountError: array_merge() does not accept unknown named parameters in public_html/wp-content/plugins/wp-criticalcss/lib/WP/CriticalCSS/Request.php:119

Cannot activate

WordPress plugin that will use CriticalCSS.com to automatically generate above-the-fold CSS for your pages.

Vitalii Rizo

Loading of JavaScript resources should be done asynchronously, in a non-blocking manner, so the load time of your webpage will not be affected (it would not be delayed by render-blocking JavaScript). But using of deferring or async loading of jQuery causes lots of problems with jQuery plugins. This plugin replaces default WordPress’s JS loader with a special jQuery loader (jQl), that’s why there are no any errors with jQuery plugins.
It’s highly recommended to use any concatenate plugin, e.g., Fast Velocity Minify or WP Fastest Cache. Please, do not add jQuery to the ignore list, because this plugin fixes “undefined jQuery” errors on the console log. Also, it is allowed to use defer or async parsing of JS files.
It requires WordPress 4.1 and newer.
It is available in English and Russian.

jQuery & Plugins Asynchronous Loader

This plugin asynchronously loads jQuery and its plugins without "jQuery is undefined" errors.

WP Critical CSS vs jQuery & Plugins Asynchronous Loader