/usr/share/kservicetypes5/plasma-layouttemplate.desktop is in plasma-workspace 4:5.12.4-0ubuntu3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 | [Desktop Entry]
Type=ServiceType
X-KDE-ServiceType=Plasma/LayoutTemplate
[PropertyDef::X-Plasma-Shell]
Type=QString
[PropertyDef::X-Plasma-ContainmentCategories]
Type=QStringList
|