I think I was fairly clear, it is a binary system that has some rare exceptions.

You are describing a "Bimodal Distribution", where most but not all fall into one of two categories.

If it were a binary system, there would be no exceptions.

Saying sex is a binary is saying there are only males and only females.

In healthy examples of mammals where development has occurred normally this is true.

Intersex mammals aren't "unhealthy", they're simply different.

This whole ‘its a spectrum’ argument is like saying humans aren’t bipedal, there’s a spectrum because some people are born without legs! It doesn’t make any sense.

That doesn’t mean that society should refuse to accept, include and support people born without the ability to walk.

Make up your mind, are people who are not bipedal still human?

If they are, then obviously humanity is not exclusively bipedal and attempting to define us as such will cause problems with everyone from non-bipedal infants to the non-bipedal elderly and disabled folks of all ages.