> Male Primary Features: Penis, scrotum, and testes.
> Female Primary Features: Vagina, uterus, ovaries, and cervix.
If a trans woman gets bottom surgery to get a neovagina then that is what they call changing primary sex characteristics.
Same with testes being converted to ovaries which has existed for quite some time but as an experimental method. Only one TIM in the UK managed to go through it.
Uterus transplants exists but they're not available to people born male because of the differences in pelvis/hips and more medical research is needed for that.
Everyone is born female in the womb even with XY chromosomes so a person who is born female has a tiny penis called the clitoris which functions the same way as a person who is born male with glans.