In order to build LibreOffice with support for KDE5 (Plasma5), the following set of additional packages is required. None of them are run-time dependencies, so the packages can be built with Plasma5 support and then installed and used on a computer without Plasma5. The packages mentioned below can be obtained from https://slackware.nl/alien-kde/current/ Qt5 support: libdbusmenu-qt5 Plasma5 support: All of Frameworks.