Replace “content-area” of themes 404 page with plugin?
According to the Template Page hierarchy, https://developer.wordpress.org/files/2014/10/wp-hierarchy.png the only template page WP will load is 404.php But, you might try this in your mu-plugins: //Some function to check database to see if this URL should exist if ( ! checkIfPageExists( $_SERVER[‘REQUEST_URI’] ) ) { //Set 404 Status status_header( “404” ); get_header(); //do your custom 404 … Read more