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 …
It’s interresting because in French (my native language) female is only ever used in it’s biological aspect and after such definition you can find in a dictionary :
“familiar, offensive : woman” source
An example would be : “Bob is really horny and is looking for a female/male”
So I always though that using female in a sentence was to reducing women to their reproductive dimensions.
But English is more complex. If i understand correctly female is valid as an adjective for persons “female/male friendship , female/male artist”. That would sounds really wrong in French if translated literally. And the noun in a dictionary is “formal : woman or girl”.
So to jump back on your comment, it’s all about context and usage. “Words politics” is a super interresting topics. At the moment, probably because of the internet, we observe over really short amount of time linguistic shift due to the usage by specific groups. Sometimes it is pretty easy to follow because the groups are large and divide society such as political orientation but sometimes it stem from obscure subculture such as incel here…