Giving my reasoning bring me in this situation, there isn't so much to be confident of.
In fact I was overrating my ability to deal with this.
I doubt will be able to overcome alone this problem, really a pity being my only (and first) working Linux installation, with many activities planned on.
Will try at my best.

To be fair, that's what I did recommend, only KDE instead of full xorg.



So, there's actually mutiple ways to fix this at this point. I'm a fan of large, blunt objects, ergo my answers generally aren't pretty, but rather blunt and brutal...


Basically at this point get rid of whatever is stopping apt install -f from completing cleanly. Once apt install -f reports that all is well on the installed front, then you can install the neon-desktop, reboot, and then reinstall whatever KDE apps you're missing that you want.

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always looks odd to me like that

and if I like what I see

but most of the time it is just plain old apt I use, if that fails I go with aptitude

I usually use something like that to clean residual configs

Ok all the process finished appear without previous errors, rebooted, Info Center state I'm now on Neon 5.16.
But even if state there are updates as soon tried to fetch them Discover crashes:

Discover error

The only error in previous process was a missing firmware on Vega20 GPU, that I didn't have.

I don't really use awk enough to remember how to do the search and print column in 1 command. and it's easier to pipe than constantly be "man awk".


The reason for using dpkg is that in the state he had his machine, it's often simpler (IMO) to use dpkg instead of apt because apt & aptitude will puke too often due to issues, whereas dpkg allows you to sledgehammer through issues with less resistance. I also personally dislike aptitude, so never use it or even have it installed. I don't mind getting a little violent with dpkg.

So, anything dealing with plasma-discover is totally beyond my wheelhouse. It's literally the first thing I uninstall after installing Neon, or KDE on any OS, for that matter.

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yeap
apt < aptitude < dpkg
routine , a bashing , nuke

ah, yeah,,,

I forgot about that

apparently it is a recent bug

Timothy thanks so much for your help, no world enough to.
Firerat tanks for your support also, nice to know there are many people interested to help.
In fact I have maintained all the app already installed, so my system is in previous state just on Neon.
Need only to track this problem, just to know what did you use to manage updates?
Btw need I to disable Kubuntu standard updates?

Attempting to update by CLI

There are a lot of repositories, maybe I didn't need all of them.

If you removed the pacakge kubuntu-desktop, then your system won't attempt to get kubuntu updates. And even if you didn't, all the neon packages SHOULD supercede it due to having higher version numbers (although I wouldn't completely trust this and if kubuntu-desktop package still installed purge it).

As for updates, I use a very basic apt update && apt full-upgrade (yes, full-upgrade not truly needed on LTS systems/base debian stable. I still like it, also many of my Debian systems become frankensystems as I use 3rd party repos to get newer versions of KDE on it than Debian offers).

This are the installed "Kubuntu" packages

Should I purge them in you opinion?

None of them are necessary, so you certainly can. I might keep the wallpapers one if you like any of the wallpapers, other than that, no reason to keep any IMO.

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Ok here again.
Discovered the error in the update was resolved uninstalling

Now I completed all the updates and both apt and Discover told me I'm up to date.
To leave the correct answer apt wasn't able to perform the update even after deleting these packages, and I needed to use

After pkcon does completed his work apt and Discover are running fine.

BUT at boot after a beautiful KDE Neon login screen I find myself in Cinnamon, with a file in the desktop telling me "There was an error launching the application".
System Info told me the OS is Neon 18.04 Bionic, so no more KDE Neon.

Any suggestion to discover what error? There isn't any other info in the file.

You could try looking at system logs and/or whatever other logs you can find - it really depends on exactly what application it is as to exactly which logs are likely to help. Some applications have their own logs, but if it's a system related app, then the system logs might give a better idea of what went wrong.

If it's just a normal app, then you could try launching it from the command-line/terminal and see if it gives any better error messages. Typically in Linux things are more verbose when run from a command-line/console/terminal window, and some things may not even give any error message via the graphical interface at all.

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Was easier than expected: I simply needed to choose Plasma as DE at login.
Choosing Plasma (and not Plasma Wayland, that I suppose it's still experimental) all is running fine with no errors at all and Info Center state I'm on KDE Neon 5.16.5.

Cinnamon was the default choice but probably being not in fact installed was giving the error and providing just a basic GNOME DE.

So finished all this I'm a proud KDE Neon user, thanks for all the incredible help of this great community!

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