How to completely disable comments in WordPress using functions.php- https://keithgreer.dev/wordpress-code-completely-disable-comments-using-functions-php

disable-wordpress-commments-functions.php

<?php # https://keithgreer.uk/wordpress-code-completely-disable-comments-using-functions-php

/* PURPOSE 
 * Disable comments on ALL post types
 * remove/hide any existing comments
 * from displaying and hide forms. 
 */

/* INSTALL
 * Add into your active theme's functions.php file. 
 */

/* 1.  Disable Comments on ALL post types */ 
function updated_disable_comments_post_types_support() {
   $types = get_post_types();
   foreach ($types as $type) {
      if(post_type_supports($type, 'comments')) {
         remove_post_type_support($type, 'comments');
         remove_post_type_support($type, 'trackbacks');
      }
   }
}
add_action('admin_init', 'disable_comments_post_types_support');

/* 2. Hide any existing comments on front end */ 
function disable_comments_hide_existing_comments($comments) {
   $comments = array();
   return $comments;
}
add_filter('comments_array', 'disable_comments_hide_existing_comments', 10, 2);

/* 3. Disable commenting */ 
function disable_comments_status() {
   return false;
}
add_filter('comments_open', 'disable_comments_status', 20, 2);
add_filter('pings_open', 'disable_comments_status', 20, 2);