Wow. Apart from this gender issue (which was new to me BTW), "females" just sounds weird here in this context, as would "males" if referring to the male characters in a novel. In my experience, including high school English and lit courses, discussing books and novels with others, reading about literature and so on, you normally talk about the characters, male characters, female characters of an author or in a book or whatever. "Males" or "females" sounds very out of place here. It sounds like someone without any experience in the subject matter or someone is just trying to sound "different". I'm sure if cryme could answer here he/she would approve of this use. Need I say more? SCNR
We have six new goldfish in our aquarium, 2 males and 4 females. That would be normal usage for "male" and "female" as a noun. Or as already suggested - in police talk, although that apparently has issues. There is nothing wrong or particularly new about using "male/female" as nouns, but you can't do it everywhere and indiscriminately.
'Female characters' would also be fine and would include not only women but also girls, female talking animals, female robots, goddesses, fairies, female vampires ...
I think hm--us put her finger on it.