I get that it can be frustrating to know a deeper and more nuanced definition of a thing and come up against people using a simpler, different or "hijacked" definition: I work in computer security and enjoy playing with machine learning. Most people get a very different impression if I say I do a lot of stuff with crypto and AI from what I mean. They hear finance bro and wasteful chatbots, and I mean user authentication, privacy and statistics.

A big point of friction I see is that it seems you're reading the words people say, interpreting them as though they're coming from the same background as you, and then responding in their terms.

If one more person tells me that "all gender is performance"

There is frustration that is generated by the "gender is just a social construct".

hour long lecture from an academic on how gender is actually just a social construct

The "performance" and "just" a social construct interpretations are what you're bringing, not the person typing.

Being told gender, that you had to struggle to find a way to make right, is reducible to how you were socialized or choose to act flies in the face of the existence of trans people and the difficulties they invariably have and is justifiably infuriating.
That the message is being given by people who very clearly, in both intent and action, believe the exact opposite should make it clear that there's a dictionary mismatch somewhere.
I feel like it stems from the belief that "social construct" implies "social constructionism".
Social constructionism is a specific theory involving social constructs , and acknowledging the existence of a social construct doesn't imply acceptance of that theory.

I don't think any reasonable person would argue that law is anything other than real by fiat of convention or collective agreement, but someone could easily disagree with the notion that scientific discovery is more about social convention than empirical reality.

Most people mean it in the sense that the WHO means it: https://www.who.int/health-topics/gender#tab=tab_1