What I get from this is that gender is supposed to be a feeling, some inner essence you are born with and aware of, which is independent from both your physical body or social expectations.

It sounds a lot like the concept of "souls" to me. This really is similar to a religion, in a variety of ways: the borderline worshipping of certain figures, the "do not question, otherwise you're a sinner/bigot" mentality, the vagueness with which they explain their core principles, leaving room for interpretation according to what fits best in the moment, etc. And now this soul, pardon, "gender" business, which is both an integral part of a person's identity, and completely unexplainable and unmeasurable. At this point, they should start writing their Bible, to at least gain some semblance of consistency.

At least, people who insist that sex and gender are the same thing, are coherent in their arguments. You can actually have a debate with most of them.

I'm also amused that this person is angrily chastising others for confusing gender with "gender roles/stereotypes", but never actually explains the differences between them (outside from a vague "it's in your head, thus obviously real"). It's like they know their arguments hold no water, but hope that if they're super confident and definitive about them, it'll fool people. And I guess, based on the upvotes, that it worked (mostly).

Edited to add that it's very sneaky how they try to frame questioning gender as reducing people to their sex. Like "terfs" are trying to convince people we're just all a bunch of walking genitalia.