Oh dear. You seem like a nice person, if a little self-important, but you've been given some very wrong information about us. Let's take a step back and unpick a few key misunderstandings.
what it is about the existence of queer people that makes you feel so threatened
The first one, the big one, is that. Some people are undoubtably threatened by the existence of queer people. They are typically coming from a place of toxic and rigid social gender stereotypes which they attach to the two human human sexes. They are the people who react with hate and sometimes violence, who you perhaps feel are trying to push you back in your box.
But we are not those people.
We believe toxic and rigid social gender stereotypes are a bad thing. People's bodies exist. Male and Female are body types with different baseline capabilities and as things stand social advantages or disadvantages due to a sexist society but that is all. They say nothing about what personality someone should have. They just are.
So we are not threatened because queer people exist. Many of us are what you would consider queer, although we may not choose to label ourselves that way.
What threatens us as female-bodied people is not the existence of queer people, but a recent, politically motivated movement that has repainted queer acceptance from what it should be, an open-minded acceptance of difference and a rejection of gender stereotypes, into a rigid and repressive insistence that gender identity does not just stand beside physical sex as an entirely separate and unrelated aspect of a person, but replaces it socially, legally and politically in every way.
And we, who know what it is to have a female body in a sexist society and so understand why the single sex provisions that exist were originally put in place, cannot accept that.
Trans people's existence does not sadly solve society's sexism. So it is not fair for the genderist movement to demand that female people give up our ability to name, fight and organise around our expreince of sex-based oppression, which is different to gender-based oppression, or else be branded unfairly as transphobes.
There must be a better way.
Every trans woman before she medically transitions presents masculine, and driving some sort of arbitrary standard of femininity
You are confusing Masculinity and Femininity, which are aspects of personality, with the simple fact of body sex. That's not your fault. The people who have "taught" you have deliberately taken the words that meant sex - Man and Woman - and appropriated them to label gender, thereby making it impossible to even frame the discussion about how sex and gender intersect. You might want to consider why they have done that.
But for now, just remember that the genderist movement created an idea that Woman is a state of mind, an identity. It is only this definition that allows the possibility of gatekeeping and misgendering. If you just see woman as a type of body that says nothing fundamental about the identity of the person who is it, the whole issue goes away and we can get back to accepting people as people. The whole thing you rail against is a false flag set up by the people who claim to be on your side.
As I said before, to people who separate sex and gender properly, Womanhood is just a fact about someone's body. Under that definition, male people cannot be women it's true, but since Womanhood is just a fact of the body, that is not a rejection of anyone's identity, it's just a recognition of an aspect of their body that may at times be significant. It's no more "arbitrary" or "gatekeeping" than saying short people cannot be tall is.
The fact remains is that trans people have always been with us, for as long as there has been recorded human history (the Priesthood of the Sumarian Goddess Inanna, for example, were non-binary and trans, and they lived and worked over 8,000 years ago)
Oh sweetheart. The fact that we know they were "trans", which is just our modern word for people who seem to cross what we think of as gendered social roles, is proof that these people's gender identities (again applying a modern understanding which is unlikely to reflect how they themselves saw themselves) were NOT considered interchangeable with femnale people but as a different group that shared some gendered social roles with female people while being understood as male. And that is fine! That is exactly the sort of place we should be heading towards. A place where we understand and accept that the social aspects traditionally coded by sex can be open to everyone, alongside acceptance that for female people especially, the capbilities of our bodies and the hangover of millenia of sexism mean that sometimes we need our sex to be recognised and supported, and that that is ok.
It's not an act of hate, and it's not a rejection of trans people. The only thing that makes it look that way is the trans movement's own insistence, through the appopriation of the words Man and Woman and thereby all pre-existing associations both gender AND sex, that sex is somehow both related and unrelated to gender. All you need to do is realise that they do not have to be related at all, and all this angst simply evaporates.