releases a frontend to Fediverse, citizens of Orange Site are concerned

It still sounds like a legitimate question to me.

It is a legitimate question. But it's a legitimate question answered in 978 pages in the late 1940s[0] – and that answer's validity is questionable, considering how much it leans on the experience of upper-middle-class French women from the 1940s. I think it's fair to say that a more complete answer would be longer.

Expecting somebody to answer this question, in the context people like Alex are asking it, is like saying "if red isn't Fe₂O₃, then what is red?" (and then refusing to listen to answers like "apples are also red" or "red is a kind of visual perception" or "photons can have different energy levels"). It's so much easier to pose the question than answer it; you basically have to be an academic philosopher to even understand why the question is meaningful.

Also the comparison to transspecies people. So a person who feels like a lion, is still a human, or not?

This, likewise, probably requires a book to answer. I'm not aware of anyone having written one; if there are academic treatises, they'd probably start by distinguishing between species concepts[1] and work from there. (I'll give the tentative answer "Yes, but it requires you to decouple some of your notions about what human is." – provided you don't quote me on that.)

A good rule of thumb to use is the principle of charity: nobody's claiming anything absurd.

So why can a person who feels like a woman change their biological s*x then?

Empiricism. Like with species, there are several different ways to define biological s*x; most can be altered, in humans. Endocrinological s*x, secondary s*x characteristics, primary s*x characteristics… Reproductive capacity, even, though that's not legally available for humans yet, and I doubt it's practically available either.

But, as you noticed, "change their biological s*x" isn't the point of being transgender. (Not that there's really "a point" in the first place, but semantics.) It might be worth making the distinction between transgender and transsexual, while observing there's a decent overlap… though there's an extent to which that's just a model, too. The best description of reality is reality itself.

There are biological differences and I don't think acknowledging that, has anything to do with supporting patriarchal power structures, which undoubtedly still exists.

There are many biological differences – but our society fixates heavily on certain differences (secondary s*x characteristics, "race"-associated phenotypical variations) to the detriment of everybody involved. It's fine to acknowledge them, but try not to categorise people by them without their consent, and don't sanctify them as immutable when they're very clearly not.

LMAO. If you can't explain it you don't fricking understanding it and neither does an 11 year old girl you fricking ghoul.