I started with:
Host: Dell Precision M3800 A10
OS: Linux Mint 20.1 x86_64
Kernel: 5.4.0-77-generic
Uptime: 2 hours, 27 mins
Packages: 2387 (dpkg), 12 (flatpak)
Shell: bash 5.0.17
Resolution: 3840x2160
DE: Cinnamon
WM: Mutter (Muffin)
WM Theme: Linux Mint (Mint-X)
Theme: Mint-X [GTK2/3]
Icons: Mint-X [GTK2/3]
Terminal: gnome-terminal
CPU: Intel i7-4712HQ (8) @ 3.300GHz
GPU: NVIDIA Quadro K1100M
GPU: Intel 4th Gen Core Processor
Memory: 3183MiB / 15913MiB

And I attempted to install the following:
sudo add-apt-repository ppa:kubuntu-ppa/backports
sudo apt update
sudo apt install kde-plasma-desktop

I received numerous dpkg (--configure) errors which seemed to me to revolve around phonon4qt5:amd64 and libkf5notifyconfig5:amd64.
I attempted to configure libkf5notifyconfig5:amd64. but I question the success of this attempt.
Scrolling back through my terminal I noticed that I had installed both kde-plasma-desktop and plasma-desktop???

I now have a miniscule Plasma desktop installed, I need to magnify to read the font. I have opened konsole but I'm unable to get it to Full Screen (F11)?

I received these suggestions and recommendations after the install which is new to me.
Suggested packages:
orion-gtk-theme tk | wish dolphin-plugins go-mtpfs kdeconnect konq-plugins
lrzsz kwin-addons fam gpsd qt5-qmltooling-plugins
phonon4qt5-backend-gstreamer
Recommended packages:
kimageformat-plugins kio-extras ffmpegthumbs kdegraphics-thumbnailers
kwin-x11 sddm libqt5multimedia5-plugins qtvirtualkeyboard-plugin
qml-module-qtquick-virtualkeyboard javascript-common kactivities-bin
libkf5baloowidgets-bin libkf5dbusaddons-bin kpackagelauncherqml
libkf5iconthemes-bin kwayland-integration libkf5kdelibs4support5-bin
libkf5khtml-bin libkf5parts-plugins qml-module-org-kde-runnermodel
sonnet-plugins qtwayland5 kde-config-screenlocker libvlc-bin libproxy-tools
bluedevil breeze-gtk-theme fonts-hack fonts-noto-hinted fonts-noto-unhinted
ibus-data kde-config-gtk-style kde-config-sddm kde-style-oxygen-qt5 kgamma5
khelpcenter khotkeys kinfocenter kmenuedit kscreen ksshaskpass ksysguard
kwin-x11 | kwin kwrited libpam-kwallet5 plasma-browser-integration
plasma-discover plasma-pa plasma-thunderbolt powerdevil systemsettings
user-manager qml-module-org-kde-kcm appmenu-gtk3-module ksysguardd

I'm wondering if my solution lies within one of these lists or whether I should abort and uninstall and then attempt a reinstall?

I'm sure there re some here who could offer some advice.

TIA, nog

Scrolling back through my terminal I noticed that I had installed both kde-plasma-desktop and plasma-desktop???

Yes, these are meta-packages, basically just listings of dependencies to be installed as a group.

kde-plasma-desktop is pulls in a minimal but fully functional plasma install.

Your problems are definitely related to the things that did not get installed, those suggested packages at the very least, plus whatever bit that is preventing them from being installed to begin with. Many off those are core components.

Without seeing some specific error messages related to the failed package installs, it will be difficult to diagnose, and will be highly distro-specific, so there will be less knowledge available about your specific problem. As many Mint users have installed Plasma successfully, their support might be quicker. I am not familiar with what Mint changes from a stock Ubuntu that might cause this sort of thing, but often stray PPAs one has added, particularly for things like drivers, Mesa, etc, can cause conflicts


For what it is worth, there is essentially zero reason to add that kubuntu PPA, as it is only useful for non-LTS Ubuntu versions (you have 20.04 LTS as your base), and in any case, you would want to make sure you have a normal Plasma desktop running before adding extra repositories anyway.