Random order

There are numerous plugins in the directory. I did a search for “random posts“.

Just make sure the plugin is compatible with your version of WordPress.

Or you can follow this tutorial “How to Display Random Posts in WordPress” (via WP Beginner)

if you want to use the existing template code without editing the index template, consider to use a 'pre_get_posts' action code in functions.php of your (child) theme;
https://codex.www.ads-software.com/Plugin_API/Action_Reference/pre_get_posts#Examples

example code (untested):

function random_order_posts_home($query) {
  if ($query->is_home() && $query->is_main_query()) {
    $query->set('orderby', 'rand');
  }
}

add_action('pre_get_posts', 'random_order_posts_home');

https://codex.www.ads-software.com/Class_Reference/WP_Query#Order_.26_Orderby_Parameters

Thanks, it works