I don't recall ever seeing that on Debian and derivatives.

I can only talk for Debian, not derivatives.

You definitely see it for several packages during dist-upgrades. Same in sid/testing except it can be any time though it's a rare event.

In case apt/dpkg is configured to ignore those, information still resides in /usr/share/doc/<pkg>

it'll also be put in the release notes when the next major Debian version is released.

I mean, distributions have already figured these things out 20 years ago, but I guess users nowadays expect these to be announced in Twitter or a pinned Github issue or something :-<

Me neither in Sid - I guess they installed the listchanges package some time and forgot.

It is marked as 'Priority: standard' thus installed as part of the standard Debian installation and shows only NEWS entries by default without needing further configuration.