pacman -Qqe | grep meta should do the trick.
-q suppresses the package version
-e filters explicitly installed packages (no dependencies)
grep filters the meta packages, assuming they follow the naming convention
-g does not help you here, because
plasma-meta is not a package group, but a metapackage.
Groups vs. Metapackages
Groups and metapackages are a solutions to a similar problem, but technically they are very different:
- A group is a logical group of packages. When you install a group, each package that is contained in the group gets installed. Groups are a concept supported by your package manager
- A metapackage is an empty package (i.e. no files are installed) that depends on a bunch of packages. When a metapackage is installed, each dependency gets installed. This does not need special support from the package manager
Because metapackages look just like normal packages to pacman, you have to rely on the naming convention with