With the help of Sune Vuorela I was able to patch some workarounds into libkscreen 4:5.26.90-3 and the compilation made some more progress but still fails:
https://people.debian.org/~coucouf/ukui-settings-daemon_3.1.1.1-1_amd64-2023-01-25T15:02:13Z.build xrandr-manager.cpp: In member function ‘void XrandrManager::monitorsInit()’: xrandr-manager.cpp:1200:50: error: ‘isPrimaryChanged’ is not a member of ‘KScreen::Output’ 1200 | connect(output.data(), &KScreen::Output::isPrimaryChanged, this, [this](){ | ^~~~~~~~~~~~~~~~ xrandr-manager.cpp:1292:47: error: ‘primaryOutputChanged’ is not a member of ‘KScreen::Config’ 1292 | connect(mConfig.data(), &KScreen::Config::primaryOutputChanged, | ^~~~~~~~~~~~~~~~~~~~
