Jeez, then you simply install the keepassxc-full package and move on. It's not like you store your sudo password in keepass database, too.
Current users will have their install broken and need to google to figure out what is going on.
Future users will install `keepassxc` thinking it would be actually KeePassXC before potentially realizing its a minimal version.
Personally I think splitting it into `keepassxc-full` and `keepassc-minimal` would be better since it moves the choice to the user instead of implying the contents.
apt shows the NEWS file during update when there's a change. If it doesn't (ie. user set it up to blindly do the upgrade), you can still check the news file or .debian.changelog.gz file afterwards.
And note that this happened in testing/sid channel, where breakage is supposed to be happen. When this change shipped in the new major Debian stable release in a few years, it'll surely be clearly written in the release notes.
What else do you expect, SMS notification? :P
If a user haven't seen the above he for sure won't see an announcement in a crowded debian-whatever-announce mailing list he isn't subscribed to or an obscure blog post posted somewhere he doesn't follow.
If it doesn't (ie. you set it up to blindly do the upgrade), you can still check the news file or .debian.changelog.gz file afterwards.
Lastly, when it's shipped in the new major Debian stable release in a few years, it'll surely be noted in the release notes.