you can fit the stereotypes for your sex but be trans
What do you mean by that? Wouldn't that mean you were born with female sexual equipment and act like a stereotypical female? I thought that was CIS. Or are you referring to someone who had surgery to change their sex?
I'm not sure who "they" are in your sentences, but I personally consider myself a male because I have male equipment. I could have surgery and change that, but I didn't. It has nothing to do with my identity, personality, sexuality, self-view, demeanor, philosophy, or anything else. I was born with a certain anatomy and I'm okay with that. I don't fit gender stereotypes, and that took longer to get comfortable with especially with the bullying in my youth. But I've come to terms with that too.
Other people have their own experiences and situations, so what feels right for me may not feel right for someone else. If they want to alter themselves and change their configuration, they are welcome to do so. I'm just describing my personal experience which may be different than other people's.
I say "feminine" for lack of a better word. I'm not trying to be a "woman" and don't wear women's clothes but my default personality traits, preferences, and demeanor are closer to that end of the spectrum, what most people consider feminine and what most people think of as not masculine. I'm also capable of being more assertive, but that was a learned skill and not my default way of being. In the end, I'm me, whatever you want to define that. I'm not trying to be something else. The word "feminine" is used to give people a reference point, not used to define me.
And there are also people like me. I am feminine and have male anatomy. I don't feel the need to have surgery to conform to other people's gender stereotypes. I am a feminine man. People just have to deal with the fact that not everyone conforms to society's stereotypes. And, while I respect other people's right to alter their bodies how they see fit, I don't think I should change my body just because someone says men aren't supposed to be feminine.
Another thing to consider is that humans have a brain powerful enough to override human instincts. For example, we are born with an instinct to reproduce, but we can choose not to.
This also applies to our sexuality, personality, gender, behaviors, preferences, and more. We don't have to conform to instincts, norms, or stereotypes.
Since that is the case, unless you're strictly talking about anatomy, two sexes aren't an accurate way to describe human sexuality.
I don't think that the problem is saying that there are "two sexes." The problem is that many people who say that tend to assign a specific gender or stereotype to that sex. In other words, what they really mean is that "men are supposed to be one way and women are supposed to be another," with the implication that someone isn't a real man or women if they are not that stereotype. That notion dismisses the reality for people who do not conform to those stereotypes. Trans people are the most obvious expression of gender fluidity, but I think most people don't conform to society's rigid standards. They just hide behind a mask, and if they are lucky, express it in the bedroom with a trusted partner.
But, as someone who does not fit gender stereotypes, I can say that there are only four anatomical configurations that people are born with: female genitalia (vagina), male genitalia (penis), both male and female genitalia (vagina and a penis) and no sexual genitalia. Most people are the first two. It also should be noted that a person can have surgery to alter this, and that babies born with both genitalia usually have surgery shortly after birth so they only have one, not both.
So a lot of the reaction to that statement is what people are reading between the lines, and not those specific words themselves.
A legitimate reason might be that you want to talk about things that your employers might not approve of, like your sexuality or your politics. We don't want to get fired because we are are LGBTQIA+ or oppose tyranny.
Personal computers used to be widely used because it was the only way to get online. We now have a new generation of users who use their phones to access the Internet and owning a computer is no longer required. Almost everyone has a phone. Not everyone has a computer.