There are tons of potential answers to all your questions, so I'll give the first ones that have risen to the top of my head while reading your post. Some answers will be in the form of analogies, or questions which I believe you will be able to answer for yourself.

Question 1# If female is something that makes eggs and male is something that makes sperm, then are kids sexless? A newborn can not produce sperm. If pre-pubescent kids are not sexless, can you tell me why?

If an apple tree is a tree that produces apples and an orange tree is a tree that produces oranges, then why are apple seeds of the genus malus and orange seeds of the genus citrus? How can a seed be an apple seed or an orange seed if it's not growing apples or oranges?

Question 2# Why are organs like penis, testes, etc male organs and why are organs like vagina, clitoris, uterus, ovaries, etc female organs? What I mean is, why can't organs like penis, testes, etc be female and why can't organs like vagina, clitoris, uterus, ovaries, etc be male? What are the reasons?

Reframe this in terms of non-human animals. Would you say a dog has a female penis or a male vagina? These categories (female and male) exist in order to describe an observed phenomenon in the physical world. The phenomenon goes as follows: lifeforms that engage in sexual reproduction tend to have two sexes (there are some wacky exceptions and complications, but they do not apply to humans because those organisms aren't similar to humans in any way except some shared DNA from back when all our ancestors were microscopic floaters in the sea), as we see with dogs, mice, a variety of plants, bees, and so forth. Female and male describe these categories even far outside the realm of gender. A snake cannot be a man or a woman, but a snake can be male or female.

These categories do not exist subjectively because observable physical processes and biological traits like DNA are not subjective.

More to the point, what words are we supposed to use to describe these observable physical processes and biological traits and patterns? If we don't see vaginas as a female sex organ, are we supposed to then claim dogs with vaginas aren't female? It leads us down a crazy path, a path in which words don't mean anything and therefore information cannot be conveyed clearly. The entire point of words and categories is to convey meaning.

Question 3# What harms do gender and non-binary cause? If gender is a social construct, why should it be abolished when other social constructs like money are not abolished? And lastly, why is being non-binary harmful?

I think the most important thing here is that many trans activists started out by claiming they were separating the notion of gender from the physical reality of sex. That didn't seem so threatening and, in itself, might not be. But now many of them are claiming that gender and sex are the same thing (as you know, based on your questions about why penises can't be female).

This has a whole host of horrible potential consequences.

I won't go into them all, but let's just pick one. Females and males often have different medical reactions to various medications and medical treatments. Females and males also present with different symptoms of the same illnesses. This has been horrible for females, because most medical studies assumed men were the default and studied males. This is why, as just one example, it's taken so goddamn long for people to realize that the female symptoms of a heart attack are very often different from the male symptoms.

If we decide to legally enshrine the notion that a penis, testes, prostate, and entire male body can actually be a female body, how the hell are we supposed to collect data on the real, observable, and life-or-death differences between male and female bodies? If we have to claim that bodies are only as male or female as the claims of the minds that inhabit them, it is verboten and, in fact, not even practically possible to study the different needs of those different sorts of bodies. And people die.

I'm sure some people would call that argument a slippery slope argument, but the entire TRA movement has been careening down a slippery slope for years so it's reasonable to assume they'll continue.