I propose that at the bottom of the F-Droid/Play Store/App Store description of the app to include a change log to indicate what has changed from the last version, which new features, bug fixes, security fixes there are.
The Delta Chat Blog can also do release announcements. I can see that some blog posts already coincide with new releases, but these are not clearly marked as release announcements, not every new release has a blog post, and these blog posts seem to focus only on selected improvements instead of listing all changes.