In the video we show you how to find the solution on your own.
Use pamac-aur to get more info about the package that reports an error.
Are there dependencies missing?
Knowing how to find the answer yourself is as important as finding the answer.
sudo pacman -S packagekit-qt5
Discover was missing a back-end. It was after all not that optional.
Extra
We explain also how to encrypt plasma to boot up fast – around 8 seconds. Unencrypted is also 8 seconds.