On multiple Ubuntu 22.04 LTS systems, I see this:
But that is not true. Not only is Ubuntu 22.04 still supported, I get updates all the time.
In the weeks leading up to April, it was saying the equivalent thing in the future tense.
Is this a bug in the KDE software update components?
$ cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=22.04
DISTRIB_CODENAME=jammy
DISTRIB_DESCRIPTION="Ubuntu 22.04.5 LTS"
This has nothing to do with KDE at all.
If you are running Kubuntu or one of the other Ubuntu Flavours, their LTS releases are only supported by their development teams for three years. The notification is correct.
Kubuntu’s volunteers just haven’t placed an announcement for this on the website.
A caveat here, though: The underlying Ubuntu OS itself - kernel, drivers, etc still are supported, so it isn’t like anything will stop working, nor will any of the software go away. So, yes, you still get updates as you see.
I am going to guess that you have both Gnome and a full Kubuntu Plasma on the same Ubuntu install, from installing the meta-package kubuntu-desktop. This would pull in the Kubuntu-specific bits and settings changes that would announce the EOL status.
I am not sure which config file provides this off the top of my head, but you can disable the notification in your Software Sources tool, or at least make sure it is set to LTS. I think Kubuntu sets it to “normal”. Yup, mine seem to be that way.
Funny, I never realized Kubuntu only has three years support.
Anyway, I’ve seen this on systems installed with Kubuntu installer, as well as Ubuntu systems that pull in kubuntu-desktop.
I guess I should report it at their end. I’m not sure if they have control over the message or only the date, because as a notice, it’s just an incorrect notice, even if it’s explainable.
Only LTS have three years, the normal releases have 9 months.
But it is correct, especially when installing kubuntu-desktop, as this partially converts to Kubuntu in a sense. It is not intended to be used to add Plasma to an existing Ubuntu Desktop as it does replace some settings, as you can see here. This isn’t really something new.
kde-plasma-desktop is the better option to use, as it does not include those things, though it is pretty minimal.
kde-standard is another option but it is on the bloated side including a lot of desktop applications, such as Kontact.
If you use Ubuntu Pro though you get 10 years of support for LTS iirc.
Let’s do some linguistic analysis:
But the reality is that Ubuntu no longer provide updates or security fixes for the desktop in this case, but agree that it probably could be made more clear for those who do non-standard/unsupported sorts of things to their systems 
. Kubuntu is part of Ubuntu, and you installed components that causes some things to report as kubuntu and/or having a three year life cycle.
The fix here is to change the upgrade setting back to what ubuntu-gnome-desktop had -’ LTS; prompts instead of ‘normal’.
But a bug report on Launchpad would be appropriate. Searching there is atrocious, and I did not quickly find a similar report, though I would be surprised that it hasn’t been done a few times over the history of LTS releases.
But the reality is that Ubuntu no longer provide updates or security fixes for the desktop in this case
How does that work? Everything I can find about Ubuntu LTS is that it’s just five years. The documentation doesn’t distinguish between desktop and server. Also, the command below shows that ‘main’ is still getting updates, and many desktop packages are from main.
Both the Muon package manager and /etc/update-manager/release-upgrades are set to lts.
I’m actually circling back to thinking this is a KDE problem. The notification screenshot seems to be generated by the ‘software update’ system settings component, judging from the icon.
Ubuntu itself thinks it’s still getting updates:
# ubuntu-security-status
This command has been replaced with 'pro security-status'.
2668 packages installed:
1640 packages from Ubuntu Main/Restricted repository
991 packages from Ubuntu Universe/Multiverse repository
36 packages from third parties
1 package no longer available for download
To get more information about the packages, run
pro security-status --help
for a list of available options.
This machine is receiving security patching for Ubuntu Main/Restricted
repository until 2027.
This machine is NOT attached to an Ubuntu Pro subscription.
Ubuntu Pro with 'esm-infra' enabled provides security updates for
Main/Restricted packages until 2032.
Ubuntu Pro with 'esm-apps' enabled provides security updates for
Universe/Multiverse packages until 2032. There are 58 pending security updates.
Try Ubuntu Pro with a free personal subscription on up to 5 machines.
Learn more at https://ubuntu.com/pro