I had an idea the other day to include a change note directly into each PR.
It shouldn’t be in the branch because that lead to lots of annoying merge conflicts. But writing it in the discussion would do. It could be prefixed by a key word like
CHANGENOTE: which makes it easy to extract. These collected notes from each PR/issue in the milestone form a good starting point of the changelog entry for a release.
Whoever merges the PR should make sure there is a change note, but it could also be written by the author or somebody else. This doesn’t need to be strictly enforced, though. It doesn’t matter if it’s missing sometimes. The release notes are manually edited anyway.
The benefit of this approach is that at the time of merging, all relevant information about this change is already aware and it’s less likely to miss details (or even get something wrong) than writing the summary weeks (or months) later.
As an additional effect this makes the description of relevant changes directly visible in the PR. Sometimes PR’s change over time and the original description is not updated. So maybe it would be a good idea to put the CHANGENOTE directly into the original post. This can only be edited by the author or core members, but others can suggest in the comments.