27. The male and female sexes, man and woman, are biological realities created by the wise will of God (see Gen. 1: 27; Catechism of the Catholic Church, 369). It is, therefore, a rebellion against natural and Divine law and a grave sin that a man may attempt to become a woman by mutilating himself, or even by simply declaring himself to be such, or that a woman may in like manner attempt to become a man, or to hold that the civil authority has the duty or the right to act as if such things were or may be possible and legitimate (see Catechism of the Catholic Church, 2297).”
https://alumniforacatholicusd.org/wp-content/uploads/2019/07/Declaration_Truths_Errors.pdf