Set post tags when post is saved based on post title and regular expression

functions.php

<?php

// functions.php is part of your child theme

function add_tags_to_post_on_save( $post_id ) {
 
  // do not trigger if this is revision only
  if ( wp_is_post_revision( $post_id ) ) {return;}

  // get the current post title
  $post_title = get_the_title($post_id);

  // apply regular expression to the title
  preg_match('/(.*)/', $post_title, $matches);

  // take the first matching group and use it as a tag, FALSE means -> do not append to actual tags
  wp_set_post_tags($post_id, $matches[1], FALSE);

}
add_action( 'save_post', 'add_tags_to_post_on_save' );