https://mail.kde.org/pipermail/kde-announce/2019-August/000047.html
Overview
The syntax Key$e]=$(shell command) in *.desktop files, .directory files, and configuration files
(typically found in ~/.config) was an intentional feature of KConfig, to allow flexible configuration.
This could however be abused by malicious people to make the users install such files and get code
executed even without intentional action by the user. A file manager trying to find out the icon for
a file or directory could end up executing code, or any application using KConfig could end up
executing malicious code during its startup phase for instance.
After careful consideration, the entire feature of supporting shell commands in KConfig entries has been removed,
because we couldn’t find an actual use case for it. If you do have an existing use for the feature, please
contact us so that we can evaluate whether it would be possible to provide a secure solution.