This is correct. There isn’t any way to get all of the values for all of the posts using any function in ACF or WP. To do what you want to do you would have to query the _postmeta table in the DB directly.
https://developer.wordpress.org/reference/classes/wpdb/
edit: in addition to this, this field in the DB only contains the ID value of the media file (upload) and you would need to get the link to this file yourself. https://developer.wordpress.org/reference/functions/wp_get_attachment_url/
