This is not an official Ubuntu package. (but it was, yesterday!)

[Birgit Edel]

This is a special case of Bug 559345 somewhere between a question and a request for better/more discoverable error message/documentation.

In apport, because thats what people encountering bugs are going to use.
In USN, because the one thing worse than no security notices is incorrect advice.
In the package changelog, because reverts are confusing enough already.

Proposed fix, among others:
Add two URLs to the apport error messages.
One to the relevant "https://changelogs.ubuntu.com/" site which apt should still know, package in Relaase or not, which hopefully by then includes a note about a package rebuild to clarify the revert.
And another one to any relevant "https://ubuntu.com/security/notices/?details=package" site, if you are able to keep the search URL stable long enough for that to reliably present a list of related USNs.

Background: `ubuntu-bug linux` will not let me report the kernel regression I ran into.. because the package went AWOL (linux-image-5.8.0-31-generic, linux-image-5.4.0-56-generic, .. see Bug 1907761)
Since I might now have two tentatively non-reproducible versions, one reproducible in between and presumably one upcoming that re-introduces the potentially responsible security backports, bisecting will be much easier with some knowledge of the order of backports applied.