The update add-on dialog that appears on launch when one of the user’s add-ons has an available update should include a changelog. Otherwise, if the user is careful, it requires going to either the repository if available or the add-on web page to glean what has been changed.
Example: the AwesomeTTS update process has historically wiped out all of the cached mp3 files. Today (2021-07-18) there is an available update for AwesomeTTS, but I won’t accept Anki’s offer to update it because I don’t know what the update includes. A changelog on the dialog would help me discern whether to accept it or not.