Gender is identity. Sex is biological. I'm considering going into a health profession, so I've studied a lot of anatomy on the side. I really enjoy therapy of the muscles, so I know the muscles and the skeleton. I'm surrounded by four posters of anatomy, as we speak, since my girlfriend is studying to become a nurse. There are so many anatomical differences between the male sex and the female sex. They are from such overwhelming differences as numbers of nerve endings in the anus, the complexity of nerves around the pelvic area, uterus, tilt of the pelvic bone, all the way to more minute differences like sizes of the scapula/shoulder blade, sizes of muscles, cardiovascular differences, placement of organs, and of course over to physiology and hormones, brain chemistry, and so forth.
These things are emulated by hormone supplements and surgery. Hormone supplements enlarges the clitoris before the second type of penis operation, where the enlarged clitoris is made to make a small, but fully functioning "penis". However, it has still the nerve-endings of a clitoris, and the urethra was moved into the "penis" by a surgeon. These are not biological changes. They're modifications. If you modify your sex, you've modified your sex. You have not swapped your sex. There are a million things science can never perfectly recreate or change. Even if we grew uteri out of stem cells and modified DNA of a pre-op trans that was put in place and was functioning, it would not be a person of the female sex.