To start, there are multiple sex determinations, and none of them includes 100% of the population. All biology tries to do with these definitions is to describe what is typical to the majority of the population, but there are always exceptions. When using the chromosomes definition, intersex people are excluded, as there are XX people who are born with male primary sex characteristics and XY people who are born with female primary sex characteristics, besides other genetic variants. Other sex determinants are the predominant sex hormones and reproductive system/gametes. These can also exclude cisgender people such as infertile people who don't produce gametes, and people with conditions that make their predominant sex hormones be the same of the opposite sex. Last but not least, it comes the sex organ, which is the primary characteristic observed at birth to determine a newborn's sex.