If a man or a woman has this complete surgery where they remove the entirety of genitalia, and I mean all genitalia, nothing is left there, do they become sexless after surgery?

And if they don't become sexless after surgery, why don't they become sexless? I thought genitalia and gametes determine sex, so when there is no genitalia or gametes, there is no sex? Saying sex is defined by genitalia and gametes would exclude a cix man or cis woman that removes the whole genitalia in surgery.

You need to use proper terminology that is "inclusive" of both sexes. Gametes come from gonads and gonads are not necessarily the same as genitals.

In humans, only the male gonads (the testes) are part of the genitals. Female gonads (the ovaries) are internal organs inside the abdomen; they are not part of the female genitals.

A woman could have her genitals and vagina entirely removed - her uterus too - and still retain her ovaries.

You question whether sex exists, but the way you frame your views and arguments seems sexist and male supremacist. You seem to think that males are the default humans, that male anatomy constitutes "the norm" for the human species.

I dunno what country you're in, but if it's the US or somewhere in the Middle East, I suggest you visit a hospital ward or rehab facility for men who've lost their lower bodies or had horrific groin injuries due to bomb blasts and combat and ask them your questions. They'll be thrilled, I'm sure, to hear that in your view they no longer are men, but have been rendered entirely sexless.