Ugly? With those lobes?

Non-native as well but for me, "female" is an adjective and only used as a noun in technical setting. If used in regular conversation setting, it's condescending and dehumanizing.

Good:

• There are fifteen females in the survey.
• The female is more aggressive, typical of hyenas.
• You bought the wrong USB cable, this one is a female.

Bad:

• This female is not very good at her job.
• You females need to tone it down.

Short answer: It's a turn of phrase the Incel movement popularized as a dehumanizing dogwhistle.

Long answer: In current American English, "Female" and "Females" are highly formal terms and really are only commonly used in situations like law and academic discourse (this is true of "male" and "males" as well, though there's much less cultural baggage associated with those terms). People who use them in casual conversation instead of the much more common "Women" (or the diminutive, "Girls") tend to be the kind of person that uses formal language to emphasize their own intellectual superiority over the common masses, and in particular all the women who won't have sex with them. In fact and almost invariably, this is presented in the form of explanations about why nobody wants to have sex with them, and the cultural forces that are causing it, and why deep down it's the women's fault they can't get a date, and it just all goes downhill from there.

edit: clarity

Female is still an acceptable term in some context: eg, when referring to the social group on a societal level, female can be fine, also for identifying someone's genetic/biological sex as "female" for medical/official contexts, that's still okay in most cases.

Where it's not okay is to use it on an individual level or to refer to a small group of ladies. The term is seem as cold, clinical, and in some cases, dehumanizing. It comes off as boiling down a person to their function in reproduction and nothing more. "You are the female and you carry children." Kind of thing. Like women are some kind of bakery for your crotch goblins, and not people worthy of respect.

But something like "the female population of the country" is fairly okay, since you're referring to the entirely of the people who identify as female, not an individual or small group of individuals.

At least, that's my take. I'm just some guy. If any women want to correct me, I defer to your judgement and opinion, and happily retract any contradictory statements I may have made. I am always happy to be corrected.