Install KDE Neon on top of vanilla Ubuntu 20.04

install-kde-neon-on-ubuntu-2004.bash

#!/bin/bash

# SPDX-License-Identifier: BSD-2-Clause
# SPDX-FileCopyrightText: 2020 Theo Markettos <git@markettos.org.uk>

# Script to install KDE Neon on top of Ubuntu 20.04
#
# The KDE Neon site says "A web search should quickly give you relevant information on how to do this. "
# but I didn't find any, so worked it out from first principles

# add the KDE Neon repository
wget -qO - 'https://archive.neon.kde.org/public.key' | sudo apt-key add -

cat <<EOF > /etc/apt/sources.list.d/neon.list
deb http://archive.neon.kde.org/user/ focal main
deb-src http://archive.neon.kde.org/user/ focal main
EOF

# pin base-files to not install the Neon version
# - this prevents the install identifying as Neon,
# and stops problems with programs that this confuses,
# eg the Docker install script 
cat <<EOF > /etc/apt/preferences.d/99block-neon 
Package: base-files
Pin: origin archive.neon.kde.org
Pin-Priority: 1  
EOF

apt -y update
apt -y install neon-desktop

This helped (now it recognizes the package neon-desktop)

but still can't install:

    Reading package lists... Done
    Building dependency tree... Done
    Reading state information... Done
    Some packages could not be installed. This may mean that you have
    requested an impossible situation or if you are using the unstable
    distribution that some required packages have not yet been created
    or been moved out of Incoming.
    The following information may help to resolve the situation:

    The following packages have unmet dependencies:
     kio-extras : Depends: libappimage1.0 (>= 1.0.3) but it is not installable
                  Depends: libopenexr24 (>= 2.3.0) but it is not installable
     libqt5core5a : Depends: libicu66 (>= 66.1-1~) but it is not installable
     plasma-workspace : Depends: appmenu-gtk2-module but it is not going to be installed
                        Depends: appmenu-gtk3-module but it is not going to be installed
                        Depends: libgps26 (>= 3.3) but it is not installable
                        Depends: libprocessui9 but it is not going to be installed
                        Depends: libqalculate20 but it is not installable
                        Recommends: plasma-workspace-wallpapers but it is not going to be installed
     python3-pyqt5 : Depends: python3-pyqt5.sip (< 13) but it is not going to be installed
                     Depends: python3-pyqt5.sip (>= 12.8) but it is not going to be installed
                     Depends: qtbase-abi-5-15-2
    E: Unable to correct problems, you have held broken packages.

So I'm going to try to install them one by one manually

The file https://archive.neon.kde.org/public.key doesn't exist anymore.

The file https://archive.neon.kde.org/public.key doesn't exist anymore.

this file does indeed exist because I literally just downloaded and added it.

It exists now. It was showing me the 404 error for some reason at the time.