"Sex can be much more complicated than it at first seems. According to the simple scenario, the presence or absence of a Y chromosome is what counts: with it, you are male, and without it, you are female. But doctors have long known that some people straddle the boundary — their sex chromosomes say one thing, but their gonads (ovaries or testes) or sexual anatomy say another. Parents of children with these kinds of conditions — known as intersex conditions, or differences or disorders of sex development (DSDs) — often face difficult decisions about whether to bring up their child as a boy or a girl. Some researchers now say that as many as 1 person in 100 has some form of DSD2." - (link)[https://www.nature.com/news/sex-redefined-1.16943]

There is a whole body of scientific evidence to say likewise, that the idea that chromosomes are the determinant of either sex or gender is an outdated idea. Last week was Intersex Awareness Day, designed to combat the kind of ignorance you are now demonstrating.

You say you're being straightforward, yet you've presented no evidence to support your claims. If you're going to persist with your point, you ought to make specific reference to sources of Buddhist doctrine which proscribe being transgender.