Well intersex could be either, both or none. Some are born with something that looks like a vagina and has balls inside of them so they think they are biologically a woman until they try to have kids and it isn't possible or are together with someone who knows what a vagina "should" look like or it looks kind of like a penis but everyone is a bit unsure. It is a big grey zone, I don't know if you can even call them biologically anything, if biologically means having one type of genitals. I am not sure if bilogical means anything either way (for intersex). It depends what you want to actually know, if you want kids then no, no biologically kids. But that could be true for someone who is what you would call biologically man or woman any ways.

So yeah one day they may discover they can't have kids or that they also have balls inside of them, or they have no balls or they have a mix of both or none. Before (and still in some countries) did the parents pick a gender and then a lot of surgery happened to make it look like a typical penis or vagina.

But it is an interesting topic, what is even sex? What do you wish to actually know? Because if it is about kids then sex doesn't matter instead it would be better to just ask "can you produce x" ( depending on what you produce). Not everyone who is "biologically" can produce what you need anyways. I know many who needed to get a sperm or egg donator (or both) to have kids.