Install KDE Plasma 5.16 on Ubuntu 18.04
 

Using Kubuntu I find annoying the Discover update behavior. In the latest Plasma 5.16 release seems to be improved, but there are no backport to 18.04. Being on Plasma 5.12.8 I suppose there are many other improvements in the latest four releases.

Discovered this instruction to install it anyway, basically using KDE Neon repository to install the needed packages on existing Ubuntu installation.

Being not an expert, want to know if I'm risking something apart some not yet discovered bug in KDE. Maybe there are specific reasons why 5.16 (and 5.15) are not supported in 18.04.

With those instruction you are upgrading your entire distribution the same as if you upgraded the current Kubuntu. You preform a dist-upgrade you may a well bite the bullet and do it with the install you already have it is the same idea. The reason the newer is not supported on 18.04 is older libraries needed updating for the new Plasma once you do that to build the newer code/install the newer packages, you are basically at the new version of the next release of Kubuntu.

Thanks really interesting!
Meaning in fact it's the same as upgrading to 19.04?
This will be a problem since some of the libraries I'm using for my work support 18.04.
I was thinking was the same as installing KDE Neon, where latest Plasma is installed on top of 18.04.

No, it's not the same as 19.04. It's the same as upgrading to KDE NEon. In fact, it IS upgrading to KDE Neon. However, the repos are still 18.04, as that's what Neon is based on.

There's also a ppa that packages the latest Plasma desktop for 18.04. I prefer upgrading to Neon, myself.

https://neon.kde.org/faq#morph-kubuntu
Seems upgrading from Kubuntu to Neon its not supported nor suggested. Any specific reason why did you prefer upgrading?
I've seen one of your systems is Neon based, how stable is in the dayly work.

I use Neon on one of my systems and on my work system. It's completely usable since other than the KDE libraries and applications it's based on LTS version of Ubuntu. And the KDE devs have gotten a lot better in the last year about catching major bugs before calling it stable. There's still the occasional minor bug, obviously, but I haven't had anything in quite some time that prevents it from running.

Reason I prefer upgrading is 2-fold, (1) I just plain don't like ppa's if I can avoid them, and (2) a reinstall takes a lot longer and I'm comfortable enough with Debian-based distro's that I'm fairly confident in my ability to recover from just about any error as long as the OS is still bootable.

Converting to Kubuntu to Neon is harder than Ubuntu to Neon. But it's still not hard, I've done it in the past. You'll just need to manually remove some things that will cause the dist-upgrade to fail (conflicting versions). Or prep ahead of time by purging all KDE (binaries, libraries, and sddm) from Kubuntu, THEN do the dist-upgrade which would go smoothly, but of course you'll be doing the upgrade from true CLI and some people aren't comfortable with that.

Not comfortable to complex operations since a beginner with just some month of experience.
Using the first post guide will be a good path, or you have any suggested instructions?
Also since I will use it for my work, there is any way to disable Neon updates to the .0 release, just enabling them at the let's say .5?

Don't understand what you're asking. Neon updates outside of KDE are simply the Ubuntu updates. KDE plasma will always follow the latest release of Plasma. If you don't want new versions of plasma, you shouldn't run Neon. It's quite literally the only reason to run Neon over Kubuntu.

Ok. Any suggested path to upgrade?

Still your 3 choices are:

1. Upgrade to Neon from Kubuntu.
2. Add the Plasma ppa to Kubuntu that tracks newer (I don't know how quickly it's updated) versions of plasma on existing Kubuntu installs. I haven't used it since I was running 16.04, so can't GUARANTEE it still exists and is still updated. But if it does, I used it on a few GalliumOS turned Kubuntu installs I used to use on chromebooks.
3. Upgrade to a newer version of Kubuntu, which you said you didn't want to do.

Sorry I didn't know how to achieve 1. :-)
BTW I already enabled this backport ppa but got only newer 5.12 release
https://launchpad.net/~kubuntu-ppa/+...untu/backports

There is no easy "1-click" solution other than "backup any important data on your system and reinstall from scratch using Neon". You've either got to just attempt it and work through the failures (there will be failures), or go through and purge all the KDE stuff installed by Kubuntu before doing the upgrade. Either of the 2 upgrade ways will require a bit of work and knowledge of the non-gui package management systems (apt/dpkg). The reinstall method will take a bit more time if you have a lot of data, but will be easy.

Sorry but I did understood option 1. was an upgrade not a new install.
As you state before reinstalling is very time consuming.
I have already used CLI many times if needed, just need a procedure to apply.

The procedure you had found and linked to in post #1 is accurate for doing the upgrade. It simply assumes the upgrade goes flawlessly, which in my experience is never true.

To do a flawless upgrade, you'd want to purge kubuntu-desktop, and also sddm, and any leftover KDE applications/libraries that are still installed before starting the upgrade.

How to purge all what is needed before the upgrade?
Also as an option what is the ppa that package the latest Plasma?