General packaging recommendations

For every KDE package you pre-install, also pre-install its optional CMake dependencies; it's okay if the user can to remove them later, but they should be installed by default
Avoid patching out mandatory or optional dependencies, as this will lead to KDE software missing functionality in ways that will be mysterious for users
Mark the `qt5ct` package in your packaging as something that conflicts with `plasma-integration` and overrides its functionality; the user should only be able to have one installed at a time, but not both!
Use the Libinput input drivers by default; don't use Synaptics on X11 as it is unmaintained and provides a subpar experience with modern large buttonless touchpads compared to Libinput

Recommended packages to pre-install

These are packages that we recommend you pre-installed by default, or install when the user installs your "KDE Plasma Desktop" metapackage.

Plasma packages

Recommended packages to pre-install:

Pre-install every package in https://download.kde.org/stable/plasma/[latest release], except for the following:

Optional packages:

oxygen5 (it's the old Oxygen Plasma theme; this doesn't need to be installed by default)

Do not pre-install these Plasma packages for Plasma Desktop:

plasma-mobile (not needed for the desktop shell)
plasma-nano (not needed for the desktop shell)
plasma-sdk (developer apps for Plasma; not generally user-relevant)
plasma-tests (internal testing harness; not user-relevant)
qqc2-breeze-style (not needed for the desktop shell)

Non-Plasma packages

These packages are add-ons, extensions, and system tools that are not released with Plasma itself, but make the overall Plasma session nicer to use. They should be pre-installed:

baloo-widgets (provides extra information for Dolphin's Information Panel when the Baloo file indexer is on)
dolphin-plugins (provides a variety of useful plugins for Dolphin, including ISO mounting)
kdenetwork-filesharing (provides the Samba file sharing setup wizard)
kdepim-addons (provides a variety of useful addons for the PIM suite; only needed if you pre-install the PIM suite!)
ffmpegthumbs (provides video thumbnailing plugin)
kdeconnect-kde (provides remote mobile phone control)
kdegraphics-thumbnailers (provides PDF thumbnailing plugin, among others)
kdeplasma-addons (provides more plasmoids)
kio-extras (provides the thumbnailing engine and many thumbnailing plugins, among other things)
kio-fuse (provides transparent access to non-KDE apps for files on remote locations)
kio-gdrive (provides transparent KIO access to Google Drive)
plasma-workspace-wallpapers (provides more wallpapers)
print-manager (provides the Printers KCM and widget)
xdg-desktop-portal-gtk (syncs font settings to Flatpak apps when run in Plasma)