I don’t think
apt can tell you on its own, but
aptitude can. Install it if you don’t have it already, then run it before your update. You’ll see a screen like this:
Actions Undo Package Resolver Search Options Views Help
C-T: Menu ?: Help q: Quit u: Update g: Preview/Download/Install/Remove Pkgs
aptitude 0.8.11 @ XXX
--- Upgradable Packages (62)
--- New Packages (2778)
--- Installed Packages (6452)
--- Not Installed Packages (202276)
--- Obsolete and Locally Created Packages (51)
--- Virtual Packages (84017)
--- Tasks (217)
The two sections will be interesting for you here are “New Packages” (which lists all packages new to
aptitude) and “Obsolete and Locally Created Packages” (which lists any installed packages which are no longer available from the repositories). Press f and Enter to clear the list of new packages; the “New Packages” section will disappear.
Now update your repositories to the new major release, and run
aptitude again: it will show the new packages and, if you’ve entirely removed the old release’s repositories from your configuration, the obsolete packages. To see the contents of a section, scroll to it with the arrow keys and press Enter; you can also use [ to expand all the subsections at once.
If you’ve already updated, and even upgraded, you can still get this information: edit your sources to point to the previous release, run
apt update, then
aptitude forget-new, edit your sources again to point to the new release, and run
apt update again.
You can track packages entering the distribution (but not necessarily a given release) by following the RSS feed for packages leaving the NEW queue. Package removals are also tracked (for the whole distribution, again not a specific release).