Hello!
I tried to install Ubuntu Desktop on KDE Neon and I got an error!
Is it an error or a bug?
Can’t say, without knowing the error message. This isn’t a bug per se, since neon is specifically a repo added to an Ubuntu core OS, and installing Gnome, or in this case a full Ubuntu implementation of it, is out of neon’s scope. So there is likely nothing that they will do to fix this sort of thing.
I can imagine there being some dependency issues from neon’s added repositories that might interfere with this.
The meta-package “ubuntu-desktop” pulls in a lot of things besides a Gnome desktop session. In my experience, a full Gnome and full Plasma desktop set up on the same system usually produces problems, anyway.
There may be a more minimal or vanilla Gnome meta-package that might work, such as gnome-session, but I have no idea what else is needed on top of that for a usable desktop.
Link of the error message:
https://drive.google.com/drive/folders/1PN2oE9GS7JfYKq6qhYyl6qQTV6zHFWov
Can you fix it?
I can’t read that very well - using a paste bin, or just copying the text here is much better.
But, I don’t think it can be fixed, not without some surgery. And likely many layers of dependency fixing. Not worth it, in my opinion.
As I mentioned, installing a full desktop meta-package is going to be problematic. Lots of small to large issues, even before factoring in third party repositories like Neon’s.
If you want to try this, then BACKUP your system. And don’t blindly trust this:
Uninstall neon-ubuntu-advantage-tools, then try again, install ubuntu-desktop-minimal for a little less invasive setup. Or just gnome-session for even less stuff.
But I cannot say how well these will work.
If you want a system where a full-on Ubuntu Gnome Desktop and a full-on Plasma Desktop on the same system, Kubuntu might be the least unsafe way to go. Enough Kubuntu users over the years have reported small to large issues installing ubuntu-desktop alongside plasma. Doing so with neon is only adding another layer of complexity to the mix.
The best way to go imnsho is to install Ubuntu proper, then install a core Plasma desktop, and not use neon at all. Just my 10 cents.
You can’t download and zoom it?
You are better off trying it the other way around install Ubuntu 22.04.3 LTS then add a /etc/apt/sources.list.d/neon.list file with its deb line in it and its gpg key located in the /etc/apt/trusted.gpg.d/ directory. Then an apt update and apt install plasma-desktop should get you its KDE packages over the outdated ones in the Ubuntu sources that are available from it. This should avoid the broken packages errors you get if you try it with the Kubuntu version as the Neon people do not use the same package(s) layout as it uses that causes all kinds of conflicts. Requiring plenty of dpkg -i --force-overwrite package_broken.deb a few dpkg --configure -a and some apt --fix-broken install to be thrown in for good measure. It was a lovely few hours of my life I will never get back the other day. But it worked well enough and it runs perfectly fine with all the up to date packages on a from Ubuntu install. Time will tell if it remains so. The packages have updated a couple of times and it keeps going, so far it has worked. If trying to use a ppa built for Ubuntu 22.04.3 after doing this you will probably get an error telling you it does not know about the Neon/user release if using that version as it installs new versions of the /etc/lsb-release and /etc/os-release files. Back them up before doing the install and copy them over the new versions that were installed.
You can’t download and zoom it?
Sure, but that is extra effort, tbh that isn’t necessary, especially if one happens to be on a mobile device or a small laptop screen. Zooming in doesn’t make the text that much more readable, and we can’t simply copy a specific bit of text we might want to search or use. Plus it makes things far simpler for you to copy the text, as well 
Just a friendly tip to make things easier for everyone. I definite did not intend the suggestion to be meant in a negative tone in any way.
KDE Neon with the base Ubuntu stuff is just… Ubuntu, no? Can you tell us your desired end goal?