Build Pokerth against Qt6.
Set QTDIR variable:

export QTDIR=/usr/lib/qt6
export PATH=$QTDIR/bin:$PATH

Before qpokerth.pro command.

When Qt6 has been built from source (e.g. Qt 6.8.2).

export QTDIR=/usr/local/Qt-6.8.2
export PATH=$QTDIR/bin:$PATH
export QT_SELECT=qt6

Fix build against Qt6 (applies to Qt 6.6, not tested with Qt 6.7.x).

uics/ui_settingsdialog.h: In member function ‘void Ui_settingsDialog::setupUi(QDialog*)’: uics/ui_settingsdialog.h:2442:25: error: no matching function for call to ‘QObject::connect(QSlider*&, void (QAbstractSlider::)(int), QLabel&, )’ 2442 | QObject::connect(horizontalSlider_soundVolume, &QSlider::valueChanged, label_soundVolume, &QLabel::setNum); | ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In file included from /usr/include/x86_64-linux-gnu/qt6/QtCore/qvariant.h:22,

ui_settingsdialog.h is an automatically generated header file during compilation.

Change line 2442

From

QObject::connect(horizontalSlider_soundVolume, &QSlider::valueChanged, label_soundVolume, &QLabel::setNum);

to

QObject::connect(horizontalSlider_soundVolume, &QSlider::valueChanged, label_soundVolume, qOverload<int>(&QLabel::setNum));