Here’s some science and evidence:
Zhou et al, A sex difference in the human brain and its relation to transsexuality, Nature, 1995: doi.org/10.1038/378068a0
Kruijver et al, Male-to-Female Transsexuals Have Female Neuron Numbers in a Limbic Nucleus, Journal of Clinical Endocrinology and Metabolism, 2000: doi.org/10.1210/jcem.85.5.6564
Garcia-Falgueras and Swaab, A sex difference in the hypothalamic uncinate nucleus: relationship to gender identity, Brain, 2008: doi.org/10.1093/brain/awn276
Savic, Garcia-Falgueras and Swaab, Sexual Differentiation of the Human Brain in Relation to Gender Identity and Sexual Orientation, Progress in Brain Research, 2010: researchgate.net/publication/49685655
Hoekzema et al, Regional grey matter variation in transgender individuals, Biological Psychiatry, 2018: doi.org/10.1016/j.biopsych.2018.01.017
McCarthy, Nugent and Lenz, Neuroimmunology and neuroepigenetics in the establishment of sex differences in the brain, Nature Reviews Neuroscience, 2017: doi.org/10.1038/nrn.2017.37
Perrot-Sinal et al, Sex differences in the chloride cotransporters NKCC1 and KCC2 in the developing hypothalamus, Journal of Neuroendocrinology, 2007: doi.org/10.1111/j.1365-2826.2007.01530.x
Speert et al, Focal Adhesion Kinase and Paxillin: Novel Regulators of Brain Sexual Differentiation, Endocrinology, 2007: doi.org/10.1210/en.2006-0845
Wright et al, Cellular mechanisms of estradiol-mediated sexual differentiation of the brain, Trends in Endocrinology and Metabolism, 2010: doi.org/10.1016/j.tem.2010.06.004
Henningsson et al, Sex steroid-related genes and male-to-female transsexualism, Psychoneuroendocrinology, 2005: doi.org/10.1016/j.psyneuen.2005.02.006
Foreman et al, Genetic Link Between Gender Dysphoria and Sex Hormone Signaling, Journal of Clinical Endocrinology and Metabolism, 2019: doi.org/10.1210/jc.2018-01105
Theisen, Sundaram and Layman, The Use of Whole Exome Sequencing in a Cohort of Transgender Individuals to Identify Rare Genetic Variants, Nature Scientific Reports, 2019: doi.org/10.1038/s41598-019-53500-y
F&S Science, Identification of rare genetic variants in the PCDH genetic family in a cohort of transgender women, 2024: doi.org/10.1016/j.xfss.2024.05.002
Hamilton, Guppy and Pitsiladis, Comment on Transgender Women in the Female Category of Sport, Sports Medicine, 2024: doi.org/10.1007/s40279-023-01928-8
Roberts et al, Effect of gender affirming hormones on athletic performance in transwomen and transmen, British Journal of Sports Medicine, 2020: doi.org/10.1136/bjsports-2020-102329
Wiik et al, Muscle strength size and composition following 12 months of gender-affirming treatment in transgender individuals, Journal of Clinical Endocrinology and Metabolism, 2020: doi.org/10.1210/clinem/dgz247
Scientific American, Is There Something Unique about the Transgender Brain, 2016: scientificamerican.com/article/is-there-something-unique-about-the-transgender-brain
Nature, US proposal for defining gender has no basis in science, 2018: doi.org/10.1038/d41586-018-07238-8
Dr Dick Swaab on gender identity and the brain: youtu.be/mOK8fw4tsO8