Started from the wpDiscuz 7.3.10 version we've added two new hooks:

• wpdiscuz_show_comments_left
• wpdiscuz_comments_left_text

The wpdiscuz_show_comments_left is designed for showing the count of the parent comments left on the "Load more" button. By default, the count is not displayed. If you want to show it, just put the hook-code below in the active theme functions.php file: 

add_filter("wpdiscuz_show_comments_left", "__return_true");

This video shows how the hook-code works:

The second wpdiscuz_comments_left_text hook allows you to change the text, that displays the number of the parent comments that are not displayed yet on the "Load more" button. This is not required, you can use it just in case if you want to change the text.

For example:

add_filter("wpdiscuz_comments_left_text", function ($text, $args) {
    if (!empty($args["comments_left"])) {
        $text = "[{$args["comments_left"]}]";
    }
    return $text;
}, 10, 2);

In this case, the default (X) format will be replaced with [X].

This article describes how to easily add custom code in WordPress: https://www.wpbeginner.com/plugins/how-to-easily-add-custom-code-in-wordpress-without-breaking-your-site/