Here's the backtrace:

Core was generated by `/usr/bin/kwin_wayland --wayland-fd 7 --socket wayland-0 --xwayland-fd 8 --xwayland-fd 9 --xwayland-display :0 --xwayland-xauthority /run/user/1000/xauth_xsjAPz --xwayland'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x00007efe0d0a140b in pthread_kill@@GLIBC_2.34 () from /usr/lib64/libc.so.6
[Current thread is 1 (Thread 0x7efe0a87ca00 (LWP 97519))]
(gdb) bt
#0  0x00007efe0d0a140b in pthread_kill@@GLIBC_2.34 () at /usr/lib64/libc.so.6
#1  0x00007efe0d041ea6 in raise () at /usr/lib64/libc.so.6
#2  0x00007efe10bc62a2 in KCrash::defaultCrashHandler(int) () at /usr/lib64/libKF6Crash.so.6
#3  0x00007efe0d041fd0 in <signal handler called> () at /usr/lib64/libc.so.6
#4  KWin::DrmPipeline::commitPipelines (pipelines=..., mode=KWin::DrmPipeline::CommitMode::TestAllowModeset, unusedObjects=...) at /var/tmp/portage/kde-plasma/kwin-6.3.2.1-r1/work/kwin-6.3.2.1/src/backends/drm/drm_pipeline.cpp:84
#5  0x00007efe108f5b58 in KWin::DrmGpu::testPipelines (this=0x5558f30f8ad0) at /var/tmp/portage/kde-plasma/kwin-6.3.2.1-r1/work/kwin-6.3.2.1/src/backends/drm/drm_gpu.cpp:450
#6  0x00007efe108f573b in KWin::DrmGpu::checkCrtcAssignment (this=0x5558f30f8ad0, connectors=..., crtcs=...) at /var/tmp/portage/kde-plasma/kwin-6.3.2.1-r1/work/kwin-6.3.2.1/src/backends/drm/drm_gpu.cpp:356
#7  0x00007efe108f64c1 in KWin::DrmGpu::testPendingConfiguration (this=0x5558f30f8ad0) at /var/tmp/portage/kde-plasma/kwin-6.3.2.1-r1/work/kwin-6.3.2.1/src/backends/drm/drm_gpu.cpp:441
#8  0x00007efe108d1609 in KWin::DrmBackend::applyOutputChanges (this=0x5558efead410, config=...) at /var/tmp/portage/kde-plasma/kwin-6.3.2.1-r1/work/kwin-6.3.2.1/src/backends/drm/drm_backend.cpp:389
#9  0x00007efe10868684 in KWin::Workspace::applyOutputConfiguration (this=0x5558f01ec6a0, config=..., outputOrder=std::optional [no contained value]) at /var/tmp/portage/kde-plasma/kwin-6.3.2.1-r1/work/kwin-6.3.2.1/src/workspace.cpp:501
#10 0x00007efe1086685c in KWin::Workspace::updateOutputConfiguration (this=0x5558f01ec6a0) at /var/tmp/portage/kde-plasma/kwin-6.3.2.1-r1/work/kwin-6.3.2.1/src/workspace.cpp:570
#11 0x00007efe10863cac in KWin::Workspace::slotOutputBackendOutputsQueried (this=0x5558f30f8ba0) at /var/tmp/portage/kde-plasma/kwin-6.3.2.1-r1/work/kwin-6.3.2.1/src/workspace.cpp:1234
#12 0x00007efe0da935b1 in ??? () at /usr/lib64/libQt6Core.so.6
#13 0x00007efe108d055b in KWin::DrmBackend::updateOutputs (this=0x5558efead410) at /var/tmp/portage/kde-plasma/kwin-6.3.2.1-r1/work/kwin-6.3.2.1/src/backends/drm/drm_backend.cpp:283
#14 0x00007efe108d01b1 in KWin::DrmBackend::handleUdevEvent (this=0x5558efead410) at /var/tmp/portage/kde-plasma/kwin-6.3.2.1-r1/work/kwin-6.3.2.1/src/backends/drm/drm_backend.cpp:191
#15 0x00007efe0da935b1 in ??? () at /usr/lib64/libQt6Core.so.6
#16 0x00007efe0dbc7ee2 in QSocketNotifier::event(QEvent*) () at /usr/lib64/libQt6Core.so.6
#17 0x00007efe0eea855d in QApplicationPrivate::notify_helper(QObject*, QEvent*) () at /usr/lib64/libQt6Widgets.so.6
#18 0x00007efe0eea9f19 in QApplication::notify(QObject*, QEvent*) () at /usr/lib64/libQt6Widgets.so.6
#19 0x00007efe0db410a0 in QCoreApplication::notifyInternal2(QObject*, QEvent*) () at /usr/lib64/libQt6Core.so.6
#20 0x00007efe0d9e64be in QEventDispatcherUNIXPrivate::activateSocketNotifiers() () at /usr/lib64/libQt6Core.so.6
#21 0x00007efe0d9e7e46 in QEventDispatcherUNIX::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib64/libQt6Core.so.6
#22 0x00007efe0e61ed9e in QUnixEventDispatcherQPA::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib64/libQt6Gui.so.6
#23 0x00007efe0db41d86 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib64/libQt6Core.so.6
#24 0x00007efe0db418df in QCoreApplication::exec() () at /usr/lib64/libQt6Core.so.6
#25 0x00005558eddedd90 in main (argc=14, argv=<optimized out>) at /var/tmp/portage/kde-plasma/kwin-6.3.2.1-r1/work/kwin-6.3.2.1/src/main_wayland.cpp:622
(gdb) frame 4
#4  KWin::DrmPipeline::commitPipelines (pipelines=..., mode=KWin::DrmPipeline::CommitMode::TestAllowModeset, unusedObjects=...) at /var/tmp/portage/kde-plasma/kwin-6.3.2.1-r1/work/kwin-6.3.2.1/src/backends/drm/drm_pipeline.cpp:84
84          if (pipelines[0]->gpu()->atomicModeSetting()) {
(gdb) p pipelines[0]
Could not find operator[].
(gdb) 


This is KF 6.11, Qt 6.8.2 and it's all built using Clang 20.1.0