We used to... somewhat attempt manual changelogs. Every time it came to a release the release manager would ask around for what the key changes were, and we usually ended up with only a couple of entries.

Now, we use https://github.com/twisted/towncrier . Every change goes through pull requests, and every PR must have a newsfragment file - and we enforce this with a test that fails if it isn't present (with convenience functions of rewriting the number to match the PR if you name the news file XXX.{category}). If it's not a user-facing change, then we just have a category that is ignored.

On releases (or on individual PRS along the way), the release manager generates the changelog, but also edits them into a relatively coherent style (or rewrites developers news fragments along the way).

Every change has a note written aimed at the user. Every entry in the changelog has a link to the relevant PR or commit. We have much better changelogs now.