<?php
function remove_title_tag_on_blog_posts($title_parts)
{
    global $template;
    $templateName =  basename($template);
    if ($templateName === 'single-post.php') {
        $title_tag_blog_post = get_field('title_tag_blog_post');
        if ($title_tag_blog_post) {
            $title_parts['title'] = $title_tag_blog_post;
        }
    }
    return $title_parts;
}

add_filter('document_title_parts', 'remove_title_tag_on_blog_posts', 10);