The Letterboxd team manually imports the miniseries they add to their website. So if you want a missing miniseries added to Letterboxd, you have to ask them directly.

As far as I can tell, Such Brave Girls is a regular comedy series. Since it wasn't marketed as a limited series/miniseries, we cannot changed its TV Show Status to Miniseries. And it is very unlikely Letterboxd would want it on their website.