Hi! It's sad that Apper hasn't received more love over the years, as it's the closest thing to a feature-complete package manager using PackageKit that we have in the KDE world. That said, even on the GNOME side, gnome-packagekit is essentially abandoned, and Apper on the KDE side would need substantial work to bring it into the KF6/Plasma6 world. Now that we have software center applications, there's much less interest in a fine-grained GUI package manager. So, if nobody is there to do the Apper maintenance work (sadly I am busy with other things :-/) then I think the only fair thing to do is to archive it.
On the Debian side, Apper won't be part of Debian 13, and if it stays archived, I'll remove it from the Debian archive for the next cycle. Best, Matthias -- I welcome VSRE emails. See http://vsre.info/