Add the metadata yourself on TMDB, get it approved (usually happens by itself) and then identify the entry in JF.
That's how I did it for https://www.themoviedb.org/tv/215216-bigger-better-baden-wurttemberg/

Edit: Upside: You help the community (mirrored to sites like trakt) and others can benefit from your work as you do from others work (metadata providers, jellyfin).

I would imagine they're indexed as movies? Try making a separate movie library for them named Documentaries and see how that goes

for german documentaries I actually made two seperate collections
one for single episode movies like this one
and one for episodic shows like Terra X or Feuer & Flamme
the later collection has the least issues scraping metadata

I just store them as regular movies and TV shows. Documentaries are a genre, not a separate media type imo.