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.

Adnan

WPBrigade

Inline JS block helps in adding above the fold JS or for your Advanced customization needs.
Note: JS Script tags are necessary to run the JS Code. So add these tags to compile your code.

Inline JS Block for Gutenberg

Inline JS block helps in adding above the fold JS or for your Advanced customization needs.

WP Critical CSS vs Inline JS Block for Gutenberg