Ok, so you need to create an ACF Field to add your title text.
It will be easier if this stores the Long title, otherwise there are some many other places where to update the other title.
Then try this PHP Snippet:
function db_swap_content_title( $title ) {
$long_title = get_field( 'your_acf_title_field' );
if (is_admin() || !in_the_loop() || !$long_title ) {
return $title;
}
return $long_title;
}
add_filter( 'the_title', 'db_swap_content_title' );
You need to update your your_acf_title_field
This in theory should replace only the content title within the loop so it will affect single and archives.