"in fall" doesn't really work in English. It's not always a 1:1 correlation, and sometimes, the best way is to just put the words out there and let people realise for themselves - like you did. Duolingo just lists the most common translations automatically when you hover over a word, and this one isn't one of the most common ones.
Btw "in" with seasons usually works in England, but sometimes implies that it will be a yearly occurrence. For example "I like going on holiday in autumn" means in the autumn of any year, "I would like to go on holiday in autumn", could be any unspecified autumn in the future, but most likely the next one, " I would like to go on holiday this autumn" is definitely the next one.
"I want to study history in autumn" kind of works, but does not specify that it is a one time thing in the next autumn, rather that in the future you would like to spend your autumns studying history.