SUMMARY

Double clicking anywhere on the Konsole scroll bar causes a crash.  This does not seem to be related to the scrollbar position or how much text is displayed, the same happens in an empty window.  DrKonqi does not start, but the backtrace from gdb is:

Thread 1 "konsole" received signal SIGSEGV, Segmentation fault.
#0  0x00007ffff52c8028 in QRasterPaintEngine::opacityChanged() [clone .cold] ()
   from /usr/lib64/libQt6Gui.so.6
#1  0x00007ffff7e0ae30 in Konsole::TerminalScrollBar::paintEvent (this=0x555555f14840, 
    event=0x7fffffffc430)
    at konsole/src/terminalDisplay/TerminalScrollBar.cpp:291
#2  0x00007ffff5ee60f2 in QWidget::event(QEvent*) () from /usr/lib64/libQt6Widgets.so.6
#3  0x00007ffff5ed6625 in QApplicationPrivate::notify_helper(QObject*, QEvent*) ()
   from /usr/lib64/libQt6Widgets.so.6
#4  0x00007ffff4d00012 in QCoreApplication::notifyInternal2(QObject*, QEvent*) ()
   from /usr/lib64/libQt6Core.so.6
#5  0x00007ffff5eb4a79 in QWidgetPrivate::sendPaintEvent(QRegion const&) ()
   from /usr/lib64/libQt6Widgets.so.6
#6  0x00007ffff5ebbade in QWidgetPrivate::drawWidget(QPaintDevice*, QRegion const&, QPoint const&, QFlags<QWidgetPrivate::DrawWidgetFlag>, QPainter*, QWidgetRepaintManager*) ()
   from /usr/lib64/libQt6Widgets.so.6
#7  0x00007ffff5ebd62e in QWidgetRepaintManager::paintAndFlush() () from /usr/lib64/libQt6Widgets.so.6
#8  0x00007ffff5ee5906 in QWidget::event(QEvent*) () from /usr/lib64/libQt6Widgets.so.6
#9  0x00007ffff72ca0ae in KXmlGuiWindow::event (this=0x7fffe80090c0, ev=0x555555dcd200)
    at kxmlgui/src/kxmlguiwindow.cpp:253
#10 0x00007ffff5ed6625 in QApplicationPrivate::notify_helper(QObject*, QEvent*) ()
   from /usr/lib64/libQt6Widgets.so.6
#11 0x00007ffff4d00012 in QCoreApplication::notifyInternal2(QObject*, QEvent*) ()
   from /usr/lib64/libQt6Core.so.6
#12 0x00007ffff4d27dd0 in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) ()
   from /usr/lib64/libQt6Core.so.6
#13 0x00007ffff4ac2ef7 in postEventSourceDispatch(_GSource*, int (*)(void*), void*) ()
   from /usr/lib64/libQt6Core.so.6
#14 0x00007fffef5723dc in g_main_dispatch () from /usr/lib64/libglib-2.0.so.0
#15 0x00007fffef575767 in g_main_context_iterate_unlocked.isra () from /usr/lib64/libglib-2.0.so.0
#16 0x00007fffef575dd0 in g_main_context_iteration () from /usr/lib64/libglib-2.0.so.0
#17 0x00007ffff4ab8510 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) ()
   from /usr/lib64/libQt6Core.so.6
#18 0x00007ffff4d28b9a in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) ()
   from /usr/lib64/libQt6Core.so.6
#19 0x00007ffff4d28eb7 in QCoreApplication::exec() () from /usr/lib64/libQt6Core.so.6
#20 0x000055555555958a in main (argc=<optimized out>, argv=<optimized out>)
    at konsole/src/main.cpp:260

The code line in frame #1 is 
        p.setOpacity(0.75);

STEPS TO REPRODUCE

1.   Open a new Konsole window
2.   Double click anywhere on the vertical scroll bar.

SOFTWARE/OS VERSIONS

Operating System: Gentoo 2.17
KDE Plasma Version: 6.3.80
KDE Frameworks Version: 6.12.0
Qt Version: 6.8.1
Kernel Version: 6.6.47-gentoo-x86_64 (64-bit)
Graphics Platform: X11
Processors: 3 × AMD Phenom(tm) II X3 705e Processor
Memory: 15.6 GiB of RAM

ADDITIONAL INFORMATION

Git bisection identifies the problem commit as e389807d, "Implement scrollbar highlighting for search results"

Settings in Edit Profile - Scrolling are:
Scrollback    Fixed size 10000 lines
Page Up/Down: Half screen height
Position: Right side
Highlighting: on
Reflow Lines: on
Colour of markers: default (#ff0000)
Size of marker: default (2%)
Colour of search highlights: default (#ffff00)
Search highlighting opacity: default (halfway along slider)