When was that? Last time I tried it was a couple of years ago.
As for the difference, outside of Spain the conjugation of Vosotros (you, plural) isn't used, but speaking to strangers is much more formal. Also, there's a lot of vocabulary differences which can be confusing for non-native speakers.
Good luck with your learning, it's a great language :-)
As somebody who doesn't naively speak Latin American Spanish but was exposed to it a lot growing up, the "th" sound for some words with "c" (like "gracias") in Castilian Spanish really disturbs me. It sounds like everybody has a lisp.
It is a lisp, albeit on purpose ... to further confuse things in parts of Spain with different languages the shared words don't necessarily have that lisp!
About two years ago for me as well, they might have rolled it out shortly after you tried or maybe I was part of some A/B testing or something. But the setting seems to be saved because I’m never given exercises with vosotros in them.
¡Gracias! Vivo en California, así que hay mucha gente para practicar hablando conmigo, pero estoy tímido y practico solo con Duolingo por ahora.
Best thing would be to go to a Spanish speaking country for a holiday, once you've been forced to use it on strangers you'll loose your language anxiety and it gets much easier (I live in Spain and work in Spanish, I'm not very good, but also no longer worried about muddling through).