This is set as "Documentary" which stands for "Series". Shouldnt it be cataloged as "Miniseries" according to TMDB? Is also the reason why it doesnt appear on Letterboxd Here what TMDB says:

Miniseries A miniseries is defined as a single-season television series telling a complete story in a pre-determined number of episodes. Event series and limited series should be set to miniseries if they have no more than 12 episodes. The "miniseries" type take precedence over the other types of TV show. Scripted and documentary miniseries should be set to "miniseries". TV movie originally released in multiple parts should also be marked as miniseries. An entry containing two or more miniseries should be set to "scripted" or "documentary" instead of "miniseries"