Is the final t in this word pronounced like an s, or is that just the synthesizer being odd?
If that is the correct pronunciation, do final t's always go to fricatives in Dutch?
The pronunciation sounds about right to me. I see what you mean about the final t sounding like an s, though for me this is still (barely) on the t side of the spectrum between s and t. We definitely don't do it like that in my native German, and it sounds very Dutch to me.
And another one that is close to German - some birds' backsides, the duck's for instance, are called "Sterz". That helps with learning.
That's just how Duolingo works. It's more efficient that way. Don't worry, Duolingo is not a teacher who will get a bad impression about you when you give an incorrect answer. Making mistakes is part of the normal process of learning a language, and in this case it's not even a mistake when you don't know the translation.
You can often get it right by clicking on the words to see what may or may not be helpful hints, and use what you already know about the target language. (When there are connectivity issues, this may not be possible.) Sometimes, though, you have to be really clever to get it right. And that's when the most effective kind of learning happens.