If the field does not need to be editable, use standard WP function to update/get the meta value, no need for an ACF field. https://codex.wordpress.org/Function_Reference/update_post_meta https://developer.wordpress.org/reference/functions/get_post_meta/
however, I would not do this. I would assume that there is something in the post that relates that post to the user. When outputting the post I would look up the get the ID value and append it to the url generated by get_permalink() https://developer.wordpress.org/reference/functions/get_permalink/ rather than create and/or update a field holding a link to the page.
