Compiling of Kronometer 2.2.1 on Kubuntu 16.04 throws an error: cmake -DCMAKE_INSTALL_PREFIX=`qtpaths --install-prefix` .. CMake Error at CMakeLists.txt:25 (find_package): Could not find a configuration file for package "Qt5" that is compatible with requested version "5.9.0". The following configuration files were considered but not accepted: /usr/lib/x86_64-linux-gnu/cmake/Qt5/Qt5Config.cmake, version: 5.6.1 Plasma 5.8.8 KDE Framework 5.36 Qt 5.6.1
Unfortunately your Qt is too old. Kronometer requires Qt >= 5.9.0 because it has an important bugfix. As workaround, you can try to install the Kronometer flatpak: https://userbase.kde.org/Kronometer#Flatpak