Sorry, I should have said, biological sex in quite a few places there - biological sex is "having a penis or not". Gender is the social construct of caring about that, e.g. deciding that one biological sex is more associated with particular traits, social behaviours, colours, fashions etc. Gender says that "blue is for boys, pink is for girls". Blue and pink have diddlysquat to do with biological sex.
So you can have a biological sex and be utterly uncaring of gender.
Re: Quotes from the book seem to state that the Radchaai have binary gender.
Gender is the social construct of caring about that, e.g. deciding that one biological sex is more associated with particular traits, social behaviours, colours, fashions etc.
Gender says that "blue is for boys, pink is for girls".
Blue and pink have diddlysquat to do with biological sex.
So you can have a biological sex and be utterly uncaring of gender.