Re: Too many distros
A bit of thinking helps here. The OP mentioned that Discover (it's KDE so why not Diskover?) somehow knew when there were new updates. How would that happen?
1. The system tray raises a notification when apt update run manually finds upgrades available so it's just watching there the results are being listed. It also raises notifications without apt apdate being run manually. That's easy to understand because
2. Cron or at are periodically running apt update, either set up by Discover itself or by the apt system - it doesn't matter which. So that
3. When the user runs the upgrade in the Discover UI all it needs to do is run apt upgrade.
In essence Discover isn't really being a package manager to do this, it's a wrapper for the system package manager.
Turning to the other side of the UI where it's supposed to check for uninstalled applications, perhaps it depends on something built in which isn't implemented properly.
But hang on - Discover isn't yet another .deb package manager, it's a KDE package manager for distros running KDE but which might have .deb, .rpm FlatPak or something else as their packaging format. So either the distro maintainers have to set it up specifically for the distro (in which case we have to look to Debian) or, more likely, it determines at run time which package manager(s) it can find and use the tools provided. As KDE produces the Neon distro (a Ubuntu spin) I'm pretty sure that if I run up a Neon instance Discover will be working - they'd notice if it wasn't which means that it can work properly with Ubuntu's implementation of apt (or it could be dpkg) but not Debian's. The error it reports looks like a network error but the reality is likely to be either:
a. A missing or differently spelled utility
b. A difference in options
c. A difference in formatting of the tool's output
If it's a. it can't be reported at install time as a missing dependency. It's dependent on one or more package management systems but they can't be declared as formal dependencies of the Discover package because otherwise it would fail to install because a distro's repository might not include package managers not appropriate to it. It really is - unavoidably - a "works for me" situation for the original developer because it needs to be tested and debugged on each distro in which it's included. What it should be doing is reporting what actual errors it encounters.
I now have a few ideas as to what to go hunting for.