Where is KDE system-wide app menu data stored:
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For the folders: "/usr/share/desktop-directories/"
For the apps themselves:  "/usr/share/applications" & "/usr/local/share/applications/"

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source: https://www.linuxquestions.org/linux/answers/Applications_GUI_Multimedia/How_To_Configure_the_KDE_3_3_Menu_manually_without_KMenuEdit?s=806324b8ca520590d60d89d6fec198a8

Date: February 2021