Comments.php

<?php

add_filter('get_default_comment_status', [
    IM_M_Comments::class, 'get_default_comment_status'
], 100, 3 );

apply_filters( 'comments_open', [
    IM_M_Comments::class, 'comments_open'
], 100, 2 );
class IM_M_Comments {
    public static $allowed_post_type = 'tutorial';
    public static $parents = [
        777
    ];
    public static  function get_default_comment_status(
        $status, $post_type, $comment_type
    ){
        if( static::$allowed_post_type !== $post_type ){
            return $status;
        }
        $post = get_post();
        if( ! $post ){
            return $status;
        }
        if( ! static::has_allowed_parent($post) ){
            return $status;
        }
        return 'open';

    }

    public static function has_allowed_parent($post ){

        $hasParent = ! empty( $post->post_parent ) && is_numeric($post->post_parent );
        if( ! $hasParent ){
            return false;
        }
        return in_array($post->post_parent, static::$parents);
    }

    public static function comments_open( $open, $post_id ){
        $post = get_post( $post_id );
        if( ! $post ){
            return $open;
        }
        return static::has_allowed_parent($post);
    }
}