Add custom separators to the Yoast SEO options

yoast_seo_title_add_separators.php

<?php
/********* DO NOT COPY THE PARTS ABOVE THIS LINE *********/

/* Add custom separators to the Yoast SEO options
 * Credit: Yoast team
 * Last Tested: September 2, 2021 using Yoast SEO 17.0 on WordPress 5.8
 */

add_filter( 'wpseo_separator_options', 'yoast_seo_title_add_separators', 10 , 1 );

function yoast_seo_title_add_separators ( $currentSeparators ) {
  $addSeparators = []; // Do not remove this line

  array_push( $addSeparators, "★" ); // Repeat to add another separator
  array_push( $addSeparators, "|" ); // Repeat to add another separator
  array_push( $addSeparators, "~" ); // Repeat to add another separator

  //Do not remove the lines below
  $newSeparators = array_unique( array_merge( $currentSeparators, $addSeparators ));
  return $newSeparators;
}