my-custom-functions.php

<?php
/*
Plugin name: Moje funkce
*/
add_filter( 'get_the_archive_title', function ( $title ) {

  if( is_category() ) {
    $title = single_cat_title( '', false );
  }
  
  if( is_tag() ) {
    $title = single_tag_title( '', false );
  }

  return $title;
});