There are various contentious statements in the introduction to the Cass report, but "medication is binary" is just baffling and meaningless.

Cass actually claims that the term "trans" has radically changed in meaning during the time the review was being written. This is obvious nonsense, and also a standard anti-trans trope.

it's also literally not. most of us all start with some level of testosterone and estrogen inside our bodies. *of course* messing with those levels below the requisite accepted threshold for a binary transition is going to allow for different results. it does in humans without HRT.