Many people consider it dehumanizing. Others interpret as a signal of at least insensitivity and at most conscious dehumanizing. It can feel threatening outside certain specific contexts and that depends much on how much you trust the person saying it.

I find it outmoded and jarring. I know people who say it as part of everyday speech and I trust them but I'd prefer it if they spoke differently and I think they're projecting an image worse than they merit.

I don't call things offensive or not, because that oversimplifies the matter. I would find "male" and "female" useful as nouns when I want to refer to biological sex specifically and not confuse it with gender. I would also find the adjectives "manly" and "womanly" useful to refer to gender instead of using "male" and "female". But as long as enough other people feel threatened by some of those words in a neutral context where they don't already trust me, it seems wise to me to be aware of that and not use those words that way.

The whole idea of saying "a white" instead of "a white man" is merely a habit we picked up from Latin, anyway.

My daughter can be pretty offensive. Quite the potty mouth for an 8 year old.

This explains it pretty well https://callmebymygender.top/

I understand your pain. My home language doesn't even have separate words for woman and female, or male and man.

Female as an adjective is inoffensive everywhere, but you will run into problems in some contexts because its definition is currently in flux and different people will mean different things by it.

Female as a noun has the same changing definition deal, and also some online misogynists use it as a pejorative. It isn't one, but they use it as one. As a corollary, some others on the internet have chosen to be offended by the term.

Not with proper hygiene.

It's as offensive as "black" is. If you call someone female that's fine. If you call someone a female, you're going to look like an incel.