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-control-center_3.0.5.1-1_amd64-2023-01-25T14:51:50Z.build widget.cpp: In member function ‘void Widget::setConfig(const KScreen::ConfigPtr&, bool)’: widget.cpp:222:47: error: ‘primaryOutputChanged’ is not a member of ‘KScreen::Config’ 222 | connect(mConfig.data(), &KScreen::Config::primaryOutputChanged, | ^~~~~~~~~~~~~~~~~~~~ widget.cpp: In member function ‘bool Widget::isBacklight()’: widget.cpp:767:18: warning: ‘void QProcess::start(const QString&, QIODevice::OpenMode)’ is deprecated: Use QProcess::start(const QString &program, const QStringList &arguments,OpenMode mode = ReadWrite) instead [-Wdeprecated-declarations] 767 | process.start(cmd); | ~~~~~~~~~~~~~^~~~~ /usr/include/x86_64-linux-gnu/qt5/QtCore/qprocess.h:168:10: note: declared here 168 | void start(const QString &command, OpenMode mode = ReadWrite); | ^~~~~ mv -f libshortcut.so ../../libshortcut.so widget.cpp: In member function ‘void Widget::setActiveScreen(QString)’: widget.cpp:1221:21: warning: operation on ‘enableCount’ may be undefined [-Wsequence-point] 1221 | enableCount = (output->isEnabled() ? (++enableCount) : enableCount); | ~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
