You are confusing sex and gender. Sex is the biological reality (male, female, intersex, etc) but gender is fully a social concept not a biological one.
What you're describing about gender is.... not really scientific. It was basically declared by fiat by researchers. It's not an authoritative definition and many people disagree with the concept, at least when it gets conflated with scientific topics.
It's a sexist concept more than anything. Basically saying that women and men should present and behave within a narrow set of parameters. Sexist stereotyping, but wrapped in progressive-sounding rhetoric.
> Basically saying that women and men should present and behave within a narrow set of parameters.
I think you're putting words into peoples mouths there.
Acknowledging that there is a social construct we generally know of as "gender" and acknowledging that certain stereotypes and common understandings of that concept exist is not at all the same thing as demanding that people should fit into the narrowest stereotypes that you can think of.
Also worth noting that you acknowledging the existence of sexist stereotyping is an acknowledgement of the existence of gender as a social construct.
There are both descriptive and normative uses of gender. To use a less charged example, it's not prescriptive to identify as American. It's not prescriptive to say other people identify you that way, even if your passport says Canadian.
An example of using the category normatively would be saying someone isn't American because they burn the flag. My experience is that most of the people using "gender" normatively don't differentiate it from sex.
This is a motte and bailey though. A regular person on the street has never seen a distinction between these two words, and common sense prevailed after years of Silicon Valley policing of speech to try to make an unpopular position seem tenable and widely agreed upon to get the average person to step in line.
Are you seriously trying to claim that e.g. wearing dresses or liking the color pink is somehow fundamentally tied the the genitals in your pants or the chromosomes you have?
The idea that gender is a social concept is so blindingly obvious that, like op I kind of assume that anyone making comments like yours about "common sense" is either blindly parroting talking points without thinking about them, or arguing in bad faith.