It's pretty simple - sex is basically your reproduction capabilities (in biology even this is far from trivial "A or B") while gender is more like how you see yourself, how you present to the world, and usually comes with certain assumptions and roles from the society you're in. That's why people say it's a social construct; it's literally constructed, socially. Being cis or trans just means whether your reproductive traits match your socially constructed traits.
Oh now I understand, thank you. I think the far right don't understand and think that people are referring to their sex. Maybe their social circles are socially/culturally separated by sex?
They definitely don't understand, but more importantly it doesn't matter either way - having a group they can persecute is just how they reinforce in-group ties. They lack a coherent ideology, and simply bond over cruelty. Any hatred that can safely be stoked will suffice for such people. Every time we accept an out-group into normal society, platform and protect them, they find new prey. Whenever we give up ground and let peoples rights get taken away, the 'far right' go back to hating them too. Cruelty is the point, and it's what turns them on. That's what makes them 'far right', is that it's obvious compared to normal conservatives.
It's just a general quality of the political far right the world over. They don't like people that don't act, look, or think like them. Anything that challenges their beliefs about what a person is supposed to do is something to fight against for them.
I think it's important to point out here that you aren't talking about gender identity (physiological), but the social construct aroundgender roles (socisl/cultural).
Gender identity is not a social construct, and I believe this is more what we are talking about when it comes to gender because the person in the article is talking about how they were born female but identify non binary.
Intention was to encapsulate the psychological aspect within the phrase "how you see yourself". It's hard to get every detail into a simple explanation.
But there's no "biological" reason for that. In the same way, skirts/dresses being for women and suits/ties being for men, leg hair, haircuts, voice, mannerisms, emotional availability, all get tied one gender or another.
We, in our society, have associated some properties to one of two genders. Some of these properties tend to be associated to one sex (sex being a more "biological" thing (but still not binary or unchangeable!)), but many of them are just expectations we put upon people. This is what "gender is a social construct" means; that the general understanding and intuition about gender is constructed by the society in which we live. Different societies may have more than 2 genders or completely different sets of associations.
Unfortunately these categorizations are bad for a significant portion of the population, including trans people, gender non-confirming people, but even cishet people; how many times have you heard of some act making you "not a real man" (eg crying for a movie)?
In lefty circles such as most of Lemmy, "gender" refers to the social norms and expectations that are attached to sex.
Personally, I think choosing the word "gender" to describe gender roles was a mistake. A call to abolish gender norms seems pretty reasonable, but if you're uninformed about this definition the call to abolish gender sounds utterly deranged.