The word "cisgender" was coined in English in 1994 in America by graduate student Dana Defosse, but the term was discussed much earlier, in German in 1914 in relation to sexology, where the habit of wearing "gender-conforming" clothing was described as "cisvestitismus" whereas cross-dressing was called "transvestitismus".
I find it interesting that academics studying gender and "gendered behaviour" decided to describe people's appearance, what they wore, in this way. Academia has a lot to answer for, but describing in technical terms how people "express their gender" through dress could so easily have been just an academic exercise, never affecting the lives of ordinary people. It might have been a minor ripple in social history instead of the huge shouting-match it's turned into.
Thing is, what a person chooses to wear doesn't really affect others. It's a person's behaviour that has an impact, not their clothes. So if people want to wear clothes that make a statement, clothes that represent their concept of themselves, fine. Women can wear trousers or whatever, men can wear skirts or kilts or dresses. It doesn't matter. It's dressing up.
It is a giant step from wearing clothes a person likes wearing, to them insisting that wearing those clothes gives that person a new identity, a different "gender". Then, insisting that other people respect and acknowledge the new identity. Insisting that other people must see them as being the new "gender". Saying that people are disgusting bigots if they question this ideology in any way. And going further, insisting that everyone use the terminology invented by the "new gender" ideologues, and use the terminology to define their own "gender", their own identity. Or else. If other people fail to use the ideological terms, they must be punished, shunned, shamed.
No. This weird fantasy is ending. I'm one of the other people, and I don't agree to be defined by those terms. I don't want or need a "gender identity". I am not "cis", nor am I "trans". (It's just a fact of life.)