All humans, with the exceptions of a tiny minority with disorders of sexual development (DSDs) or Intersex, are either male or female. So there are two sexes.
We are not tilapia, frogs or molluscs, and these sexes are fixed for life. Sex can never be changed. The nonsense that biological sex has no basis in reality and can be changed from male to female is just that, nonsense. It derives from Post-Modernism; a rotten, toxic ideology. But that means we must explain the phenomenon of transsexualism, and to do that we’ll focus on the form found in Luzon in the Philippines, the bakla.
The explanation hinges on the critical difference between sex and gender. These are not the same.