I use several Linux-based computers, which include an older machine running Debian / Jessie and the KDE 4 desktop manager, and a more-recently-installed machine, running Debian / Stretch and the Plasma 5.8 desktop manager.
Under KDE 4 – which I’ve grown used to over the years – the K-Menu – aka, the Application Launcher – would display a nested menu-system, that included the KDE categories into which applications should fit, which are defined essentially by ‘.desktop’ files, plus a separate category called ‘Debian’, which was denoted by a folder-icon, and which was nested several levels deep, into which almost every installed application should be sortable, defined essentially by the contents of the directory ‘/usr/share/menu’.
Under my Plasma 5.8 setup, one fact which I was missing, was the earlier presence of this Debian -category:
Instead, this computer has a larger abundance of entries, in its Lost+Found category (not shown), which is really just another way of saying, ‘entries which it cannot otherwise put into categories’. In fact, many of the entries that now occur under Lost+Found, also occur under listed categories.
(Updated 12/14/2017 : )