In The Culture series by Iain Banks, gene modification is so advanced people can will themselves to change sex without surgery over I think some months. The process is so effective procreation is possible - one character, a male, loved being pregnant. So he’d transition, have a baby, and go back to being male every couple years. And it’s just super normal.

Sigh

I’m happy being as I am, but if I were to live thousand years and it were easy, why WOULDN’T you change just to see what it’s like?