here’s nothing weird about Cis, it literally just means ‘not trans’. People are so ignorant.
Nope. Firstly why should anybody be described as 'not trans'? When there is a perfectly good word to describe them.
Secondly, identifying with the skin in which you are born, means you identify with the gender ascribed to your sex.
Many, many women do not. This does not make them trans.
Gender is a set of externally imposed stereotypes and expectations, where those ascribed to women are invariably detrimental to them. And those ascribed to men are not.
Imagining that gender is anything other than that, is very unanalytical thinking. Even official trans groups describe gender as societal expectations.
Ask yourself what gender is, specifically? How would you describe it, identify it, verify it?
You will quickly conclude that it is a set of stereotypes.
That is why the word cis, which asserts that you agree with those stereotypes, is offensive.