wp_get_post_terms()
https://codex.wordpress.org/Function_Reference/wp_get_post_terms to get the post categories. This will return an array and it will contain multiple categories if the post is in multiple categories, so you’ll need some way of deciding what category to use unless you make sure that only one is ever selected. Once you have the category
$hide_title = get_field('hide_title', $category->taxonomy.'_'.$category->term_id);