Could we have some other extra training possibilities to train new words, please.
Like a memory (all cards/words are visible) and we have to find word pairs. Or a verb-training, where we have to conjungate the verbs.
Is it possible to get a flash card training with animals, or only the words of one topic?
You could try Memrise or Quizlet. There is a game similar to the one you describe in Quizlet.
Both of these have ready made sets of lessons for Duo vocabulary, or you can make your own sets.
I suspect that Duo has other priorities so I was just suggesting other good alternative means of memory training.
Of course, if you want it on Duo, you may have a long wait.