KDE Linux/Install software not available in Discover/Nix

The Nix package manager is a highly advanced tool that can be used to acquire virtually any free software package you can imagine. It can be installed and used in KDE Linux like so:

# As per https://nixos.org/download:
# Install nix-shell only for the current user:
sh <(curl --proto '=https' --tlsv1.2 -L https://nixos.org/nix/install) --no-daemon
# Log out and log in again
nix-shell -p mc emacs-nox
# You are now inside a shell where mc and emacs are available

Fur further information, see https://nixos.org