What you mean is that "faut" does not stand as a verb, right? "Il faut" is an expression. Yet duolingo displays the option "conjulgate" for "faut", which makes everything very confusing. I went for "He needs to be a man" and he said it was wrong. Duolingo also added to the correct sentences: "One needs to be a man". How can "Il faut" be translated to "one needs" and not to "he needs"?!
"faut" is indeed a verb (conjugation on 3rd person singular only, but all tenses) and the subject "il" is impersonal, like "one". You may consider that "il faut" means "one must" or "one has to" or "one needs to" or "it is needed to". However the French "il" in this expression does not stand for a man "pronouned" as "he".
In a number of sentences where the French uses "on" or "il faut", Duolingo proposes different solutions to express the neutral indefinite subject. "we" is one of them, "you" another or "one" in some cases, or "it". In other words, to translate "il faut être un homme", you may have different solutions:
"we must/have to be a man" "you must/have to be a man" "one must/has to be a man" "it is necessary to be a man"
Sorry, it's not clear to me would "you must be a man" have been accepted as a correct answer? does duolingo just not display that? it seems completely wrong to accept "we must be a man" since that makes no sense in English. Seems like a bad question to me, there are better ways to introduce il faut.
It seems to me that the confusion about this sentence comes from the fact that it is quite an arbitrary construction which would almost never be used in natural language. The only situation I can imagine this being said would be to translate the English phrase 'Be a man!' - meaning 'stand up for yourself' or more colloquially, 'grow some balls/grow a pair'. In the English construction, you wouldn't need to use 'You have to/It is necessary to'. I feel this explains the confusion, but I would be interested to see if others agree with me or not.
The very purpose of this exercise is to teach the French construction "il faut" as the main construction matching "it is necessary" or "I have to" or "I must" or " I should"... Therefore, a direct translation is required, even if, you are right, there are more colloquial (even vulgar) alternatives in English.