You can tell by the language they use. Using the word "females" instead of "women." Placing a lot of emphasis on biology and evolutionary psychology. (Which they misinterpret all the time but that's not part of the scope of this discussion.) I don't think they have the slightest clue what the difference is between gender and sex. I think they completely ignore the nature vs. Nurture debate. The fact that transphobia sometimes appears in redpill also suggests that redpill guys don't understand what gender is.

Sex refers to a set of biological attributes in humans and animals. It is primarily associated with physical and physiological features including chromosomes, gene expression, hormone levels and function, and reproductive/sexual anatomy. Sex is usually categorized as female or male but there is variation in the biological attributes that comprise sex and how those attributes are expressed.

Gender refers to the socially constructed roles, behaviours, expressions and identities of girls, women, boys, men, and gender diverse people. It influences how people perceive themselves and each other, how they act and interact, and the distribution of power and resources in society. Gender identity is not confined to a binary (girl/woman, boy/man) nor is it static; it exists along a continuum and can change over time. There is considerable diversity in how individuals and groups understand, experience and express gender through the roles they take on, the expectations placed on them, relations with others and the complex ways that gender is institutionalized in society.

https://cihr-irsc.gc.ca/e/48642.html

Sex and biology doesn't dictate that women should like makeup, wear dresses, be the pursued in a relationship, have longer hair, be more submissive. Sex doesn't determine that men should pursue, that they should only wear pants, be more dominant, and so on. It is gender that determines what society says men and women do. Calling people "men" and "women" acknowledges that people are more than just their DNA and their genitals.

I'm a cis woman and I identify as such not because of the fact I was born female. It's because of how I grew up, my interests, and how society sees me. How I see myself. I like things such as fashion and makeup, but not because it's what "females" do. It's because it's artistic. I like cars and building things not because I'm trying to go against the grain... I just like seeing how things are built and designed. I was raised in a household where those who are born female are automatically deemed as lesser beings. Such a mentality is fucking dangerous because it allows for abuse to happen. And it dictates how people should live according to their sex. Which is fucking stupid... why should I waste my God-given talents for art and music and crafting things? My time is not better spent cleaning up after people and raising children. Because of gender, which is a social construct and therefore is allowed to be different for everyone.

Anyways, my story is just an example. I think that men can ask themselves the same thing. Is my boyfriend a man because he was born male? Is he good at fixing things, woodworking, and working on cars because of his genitals? No, it's because it's how he was raised. That's what he and his dad would do together.

People go against their gender every day. Women wear pants, many women want to be dominant in bed, many women are the breadwinners of their household. Some men grow their hair out, some men are stay-at-home dads, some men take on traditionally feminine jobs and hobbies like nursing or floral design. Why? Because gender is fluid. It's a social construct. It can change. People change it so they can be happy.

This is one reason why the "female nature" argument is complete bullshit.

You should ask yourselves. Were you rasied to be "male" or a "man?" Are you yourself simply because of your DNA and genitals? Or was the way you grew up and treated have an effect on you? Don't expect to be treated as masculine if you don't even acknowledge that there is more to other people than their sex. You're a hypocrite if you want to be called a "man" but insist on using the word "female" instead of "woman." Do you recognize your own gender? Why would you recognize your own gender, but ignore that the opposite gender exists? Doing so is dehumanizing.

Is sticking to old ass strict gender norms really going to make you happy?

Do you really want to live your life strictly according to the fact you were born male or female? There's really not much point to life then outside of food/water/shelter/reproduction. You wouldn't even be treated as masculine, since that's a social construct. Since logically you would have to live by the rules of biology and nothing else.

Start acknowledging that gender exists but it's a social construct that can change.

Edit: typo and added another question.