What isn't scientific (as is, no longer valid in scientific consensus[0]) is the premise that gender and biological sex are synonymous, and that, as your comment implies, transgender or nonbinary identity is a denial of science.
Just in case you're going to jump on to the title of the third article i posted below, note that it says gender is not just a social construct, rather than that it isn't such at all. I'll quote an excerpt from that article:
Evidence that gender has some basis in biology, though, in no way implies a strict gender binary, nor negates the existence of transgender and non-binary identities. Many biology-based gender differences originate from the hormonal environment within the womb, which is very different on average for boys compared to girls. But there’s a huge variation in these environments, says Alice Eagly, psychology professor at Northwestern University. “Within boys there will be a range and within girls there will be a range. To say it’s biological doesn’t mean it’s perfectly binary,” she says.
[1]https://medicine.yale.edu/news-article/what-do-we-mean-by-se...
[2]https://qz.com/1190996/scientific-research-shows-gender-is-n...
> In the 15th century gender expanded from its use as a term for a grammatical subclass to join sex in referring to either of the two primary biological forms of a species, a meaning sex has had since the 14th century