All of it. It comes down to process followed by the dev team.

But, it is done at the time of writing the PR or requirement. For eg: "Add paid subscriptions" feature request. If you have, say, a markdown document that outline the feature request, it would be a simple matter to have a script pull specific tags to build your release note. A ProdMgr would own the release note anyway. So, it doesn't really matter.

My 2 cents, anyway. Others might have a different view.