Sex and gender are different, though. Sexologist John Money came up with the idea of using the then purely grammatical term 'gender' to describe how people presented themselves.

So originally people's gender expression was more or less just advertising their sex roles for mating. Now it's more of a lifestyle/aesthetic thing with huge amounts of variation that aren't really anchored to biological sex in any meaningful way except insofar as they adopt the aesthetics of one of the biological sexes.

Do the rational tech people believe the science of gametes or do they put their faith in a different belief on how gender works?

The rational answers to both these questions is to accept we don't know (whether a fetus has a soul or how many genders) and stop trying to force whatever unproven answer we personally prefer onto everyone else. If you don't believe in abortion, don't get one. If you think there are 2 genders, pick from those. But don't act like you have some concrete proof you're right when you don't...