how to get last id in database codeigniter 4

1function add_post($post_data){
2   $this->db->insert('posts', $post_data);
3   $insert_id = $this->db->insert_id();
4
5   return  $insert_id;
6}

1   $this->db->insert('posts', $post_data);
2   $insert_id = $this->db->insert_id();
3   return  $insert_id;

1  $db = db_connect();
2  $query = $db->query("SELECT * FROM users ORDER BY id DESC LIMIT 1");
3  $result = $query->getRow();