Brains are messy things and the argument of the article linked is reductionist (as are most papers which make hand-wavy assertions that one brain is "similar" to another). MRI studies with small sample sizes such as the one linked are almost always underpowered [1]

All the study conclusively proves is that both trans women and regular women don't react as viscerally to porn as much as the average man. The actual connectivity and structure that yields similarity in activation between trans and cis women may be completely different.

[1] https://journals.plos.org/plosone/article?id=10.1371/journal...