It’s very obvious all mammals are dual sex, no more no less. It’s a fact that there are only 2 sexes when it comes to mammals. They also have average behavior differences due to hormones and their structure, but this only goes so deep. Bulls for instance are more aggressive than cows on average - this is because their hormonal differences that stem all the way back to their chromosomal differences, but also due to their body differences (like extra muscle and size) that give them the ability and perception by other cows.
These things are the same in humans: we have our “run-time sexual differences” that come from hormones, and our “static sexual differences” from how those hormones have built our bodies over time. Men behave differently on average because of the hormones profile in their body is different from that of women. Men also behave differently because those hormones over their life time have changed their body to be larger on average, and this on another level has led them to have different experiences than women that have shaped their mindset and behavior (eg being larger means people treat you differently, and that reinforces different behaviors).
All this to say that the differences between the sexes are almost entirely immutably biological at the base (including the social construct aspects). The differences between men and women start from the chromosomes, and that decides hormones and body structure, and those two affect how people treat you naturally (a larger, more aggressive organism is treated differently than a smaller, less aggressive person), which creates over time what we call gender roles.
Some examples: men being deemed “protectors” isn’t just some arbitrary gender role out of the blue, it stems from the fact that one sex of the human species is obviously larger, and so naturally expected to step up in these situations throughout their life. Aka: if you reset everyone’s memory of gender roles, they’d likely come back and be pretty similar in broad strokes very quickly, because they are determined at the base by chromosomes > hormones > body structure > how others perceive you and the experiences you have in your life as a result.
Men can never be women and vice versa. You can change the hormones, but you can’t change the body structure, the chromosomes, the experiences of the individual and others, and consequently how others naturally react to them. Those aspects all together are what makes a man fundamentally different from a woman.