I don’t think “female” is offensive.
I thought it was offensive because some (supposedly female) users said it was offensive; but I didn’t understand why my female friends used the term (female).
I found another saying that it wasn’t offensive, and I immediate copied that belief.
LGBTQ+ politics is confusing …
incels occasionally use it to depersonify women. like they’ll call men just men, and then call women females. that’s a very specific context though, so any sane person will not get offended if you use the word normally