I have a theory as to why TRAs say Gender Critical people are propping up the patriarchy. It's because they have inverted the meaning of lots of key words.
We know they use "man" and "woman" as if they denoted gender identity or gender (behaviour), not sex.
For example, what we call "sex markers" or "sex characteristics", their filter converts into sex stereotypes - more properly known as "gender stereotypes". And the corollary is when we talk about "gender norms", they hear "sex stereotypes". So when we say we can clearly see male sex markers - hips/neck/brow ridge, etc, they see that as us being unfairly focused on stereotypes.
When we say, "men can't become women", they hear "men should follow masculine gender norms". Or "you can't change sex" means to them that nobody can change break out of gender stereotypes.
When we talk about boundaries, they hear "limitations" as in limits on the person's potential or personal expression, of which changing gender is the most important to them. So "children should have boundaries" = children should be prevented from experimenting. "Women have boundaries" = women should be limited by gender roles. Hence a few years ago, on Hampstead Heath iirc, a group of young women shouting, terrified and enraged, that terfs could not trap them in womanhood - which of course means gendered roles to them.
And of course, "gender critical", ie critical of gender, becomes "gender is critical" - ie gendered stereotypes are essential.
There are other examples, which I can't remember now, but I think a different understanding of what words mean plus fear/unwillingness to hear the GC
side is at the heart of it. It doesn't help that they use "gender" indiscriminately to mean sex, gender identity, gender stereotypes and gender presentation.
So I think that is how they think we are "propping up the patriarchy".