Except that there is no such scientific proof. The few studies that have been done have been of adults, many of whom had already “transitioned” and/or taken hormones (so causality cannot be inferred). And those few studies have been refuted.

In order to prove being transgender is innate, researchers would have to do brain scans of a huge number of newborn babies who had had zero life experience outside the womb. Then those babies would have to be left alone, allowed to grow up with no one telling them they are the opposite sex (since experience molds kids’ brains). The people would have to be followed into adulthood, and then the scans from infancy compared. There would have to be some indication that the babies’ brains differed as indicated by their declared identity as adults. You’d also have to have a large control group of babies who grew up not thinking they were the opposite sex, and find a brain region that strongly correlated “felt” gender with actual sex in the two groups.

No such research has been done. No one is recruiting babies for such studies. In fact, the research that has been done shows that the vast majority (75% or more) of gender dysphoric kids outgrow the feeling of being the opposite sex and grow up to be gay or lesbian.