function my_acf_load_field($value, $post_id, $field) {
if (empty($value)) {
$value = get_the_title($post_id);
}
return $value;
}
add_filter('acf/load_value/name=character_overview_title', 'my_acf_load_field', 20, 3);
if you field has never been set then this will not work, in this case you must put it in the code where you want do show it.
$text = get_field('character_overview_title');
if (emtpy($text)) {
$text = get_the_title();
}
echo $text;