Just one anecdote, but some reports definitely get looked at.
I assume this would have landed them in hot waters with EU privacy regulators, so they were very keen to replicate the bug and then have me check if it no longer happened.
On the other hand, the "first screenshot fails to display screenshot preview and doesn't flash the screen" has been in iOS for 3 versions now. I've reported it thrice, and no one has given the tickets a second look, marked it DUPLICATE, or anything. And every time I mention it, at least 3-4 other people comment on also experiencing the bug, so I assume Apple must be pretty aware.
My suspicion is that there's a really gnarly race condition as the root cause, and they haven't been able to find it.
You will never get a response to tickets unless it is affecting a lot of people and they need more information e.g. crash reports.
They are all read/triaged though.