Disclaimer this is not a woke post but I’m just curious.
I just answered 美人 with “beautiful person” and got it incorrectly because the correct answer was “beautiful woman”.
Did some minimal research that in modern Japanese and found out this might as well be used to refer to male too? (I’m thinking of someone like 壬氏 from 薬屋のひとりごと)
I’m not immersed in Japanese that much to tell if that’s true though so any knowledge on this topic is very welcome.
The word is typically used to refer to feminine beauty, and most commonly used when speaking about women. I guess it can be used with males but the speaker needs to know what they are doing.
The description on the WaniKani page for the vocab item specifically address this, btw:
Wait, why isn’t this a beautiful person? In fact, this word used to have a broader meaning, but for some reason it’s generally only used for women in modern Japanese.
Modern dictionaries such as Jisho and JapanDict concur:
I checked 大辞林 to have a J-J source:
美しい容貌の女性。美女。麗人。〔古くは，男子もさした〕
In older settings (I think 薬屋のひとりごと counts as that) or very old literature, it might be used for males too, but in modern Japanese it’s only used for women.
Because Japan is not woke
Kenkyusha weighs in.
a beautiful ［a lovely, an attractive］ woman ［lady］; a pretty girl; a beauty; a belle; 《口》 a good-looker; a looker; a peach.
美少年 and 美男子 seem to be alternatives for boys and men.
I don’t disagree that “beautiful person” should be accepted…but in practice I have never seen or heard anyone use 美人 when referring to a non-woman. But maybe if I work hard enough someday I can inspire that sort of praise from someone (not holding my breath though)! 
I am fairly certain that the main character of this work thinks of 壬氏 as an eunuch who has a womanly charm, so it makes sense to express this by using a word normally used to describe woman. This does not mean it can be used for men in a more general setting.
After doing an informal poll via LINE, 90% of respondents said that people do use 美人 to refer to men as well…
However, when asked for examples of this, the men that were referred to as 美人 were exclusively those appearing feminine using make-up, clothing, voice, and affect (visual kei and K-pop idols were cited), so…I’m not sure that’s helpful at all, both for this discussion and also for my chances of being personally referred to as 美人. 
Thank you everyone for the replies!
From your answers, I’d conclude that 美人 in modern day Japanese is used exclusively for women and might have some usages for male too in ancient time/literature or in today’s informal situation describing anyone with feminine features.
Thanks to all of you again for your effort.