German for women
I thought that the plural of Frau was Frauen in all four cases. Duolingo has just tried telling me I should have used Fraün. Does that even exist?
You are correct in assuming that the word does not exist.
It lookes like somebody wrongly thought, that u + e would have to be written as ü, which is definitely not the case here.
The a and u form a diphtong, and while the combination äu exists in other words, I connot think of a single word that contains aü.