Functionaries and other occupations.
Is this really a word that should be in a beginner's Spanish class? At this point I would rather learn about cashiers, waiters, bus drivers, tour guides, hotel clerks, maids, and police officers than ambassadors, functionaries, prosecutors, counts, kings, lawyers, judges, colonels and authors.
I feel like David Sedaris when he was first learning French and only could say 'bottleneck' and 'social climber.'
IMO Duo is teaching us what it wants us to know to do the translating it wants us to do, not the Spanish we would like to learn for our own purposes.
So it is a case when something is offered for free, you are the product.
I am 99.9% sure I have never used the word 'functionary' in my life. And the only count I know is on Sesame Street.
There are some unusual vocabulary like you say but I have heard the word "funcionario" quite a lot when learning Spanish elsewhere.