The idea is that people read it to the bottom, then by default it is auto-unpinned. I don’t see a huge problem with the status quo at the moment, though I agree it sucks to be anon in this case.
We could hold an anon cookie to clear the pinned topics later but that feels like a complex change?
It also seems you have beef with the categories page – where excerpts are expanded by default on mobile which I agree is weird – but what is shown above is 100% latest page.