The history of someone’s experience isn’t captured by the term “biological” it is in the terms “trans” and “cis”.

“Biological sex” is broken down into different categories. Chromosomal, Horomonal and Phenotypic. Chromosomes hardly need an introduction, it’s the DNA programming that under most common conditions creates the blueprints for the other two forms. However this isn’t always how it happens.

Phenotypic sex is all the physical structures that conform to different expressions of sex. Genetailia, internal organs, differences in physical structure between male/female.

Hormonal sex characteristics is the group of chemicals the body releases to change the body and support adult maturation of Phenotypic sex characteristics. It also changes the biochemical makeup of the body, including the brain, so the body allocates resources differently and responds to things like stress and medications differently.

When a trans person goes on hormones or receives surgeries their Phenotypic structures change to conform to their new gender which mean in a real rubber to road kind of way they stop having as much medically in common with their birth sex as the sex they transitioned to. If you give a trans woman the “biologically male recommended” medication dosages of something like sleeping pills they are going to be taking way too much because that medication interacts differently with the Phenotypic and hormonal tissues of women which her body now conforms to.

The concept of “biological woman/man” is actually a fairly dangerous concept in the medical world because the assumption created by that framework often create errors of medical care expectations which put trans people in actual danger of poor dosages or completely wrong expectations of navigating their personal biology.