To clarify a bit more, it doesn't crash immediately when opening the appearance style menu, but loads some of the appearance styles and crashes within a second.

So I basically see a flash of the appearance styles menu loaded before it crashes.

Here is same stack trace with more debuginfo (installed glibc debug info)

Application: System Settings (systemsettings), signal: Aborted

[KCrash Handler]
#4  __pthread_kill_implementation (threadid=<optimized out>, signo=signo@entry=6, no_tid=no_tid@entry=0) at pthread_kill.c:44
#5  0x00007f9e07888cb3 in __pthread_kill_internal (signo=6, threadid=<optimized out>) at pthread_kill.c:78
#6  0x00007f9e078389c6 in __GI_raise (sig=sig@entry=6) at ../sysdeps/posix/raise.c:26
#7  0x00007f9e078227f4 in __GI_abort () at abort.c:79
#8  0x00007f9e07ce34d5 in qt_message_fatal (message=<synthetic pointer>..., context=<optimized out>) at global/qlogging.cpp:1914
#9  QMessageLogger::fatal(char const*, ...) const (this=this@entry=0x7ffe03942700, msg=msg@entry=0x7f9e08090b48 "Cannot mix incompatible Qt library (%d.%d.%d) with this library (%d.%d.%d)") at global/qlogging.cpp:893
#10 0x00007f9e07cf7a08 in QObjectPrivate::checkForIncompatibleLibraryVersion(int) const (this=<optimized out>, version=<optimized out>) at kernel/qobject_p.h:438
#11 QObjectPrivate::checkForIncompatibleLibraryVersion(int) const (version=<optimized out>, this=<optimized out>) at kernel/qobject_p.h:430
#12 QObjectPrivate::QObjectPrivate(int) (this=<optimized out>, version=<optimized out>) at kernel/qobject.cpp:191
#13 0x00007f9dac2cfb50 in QGtk2StylePlugin::create(QString const&) () at /usr/lib64/qt5/plugins/styles/libqgtk2style.so
#14 0x00007f9e08b21919 in QStyleFactory::create(QString const&) () at /lib64/libQt5Widgets.so.5
#15 0x00007f9dac8d73c6 in PreviewItem::reload() () at /usr/lib64/qt5/plugins/plasma/kcms/systemsettings/kcm_style.so
#16 0x00007f9e05cbe081 in QQmlObjectCreator::finalize(QQmlInstantiationInterrupt&) (this=0x55d572d22c70, interrupt=...) at qml/qqmlobjectcreator.cpp:1413
#17 0x00007f9e05c531a2 in QQmlIncubatorPrivate::incubate(QQmlInstantiationInterrupt&) (this=0x55d572c51370, i=<optimized out>) at /usr/include/qt5/QtCore/qscopedpointer.h:116
#18 0x00007f9e05c53625 in QQmlEnginePrivate::incubate(QQmlIncubator&, QQmlContextData*) (this=0x55d5726d25e0, i=<optimized out>, forContext=<optimized out>) at qml/qqmlincubator.cpp:89
#19 0x00007f9e0305174f in QQmlDelegateModelPrivate::object(QQmlListCompositor::Group, int, QQmlIncubator::IncubationMode) (this=0x55d5735f3b80, group=QQmlListCompositor::Default, index=6, incubationMode=<optimized out>) at qqmldelegatemodel.cpp:1324
#20 0x00007f9e061a7584 in QQuickItemViewPrivate::createItem(int, QQmlIncubator::IncubationMode) (this=this@entry=0x55d572965580, modelIndex=modelIndex@entry=6, incubationMode=incubationMode@entry=QQmlIncubator::Asynchronous) at items/qquickitemview.cpp:2351
#21 0x00007f9e06199355 in QQuickGridViewPrivate::addVisibleItems(double, double, double, double, bool) (this=0x55d572965580, fillFrom=-320, fillTo=908, bufferFrom=<optimized out>, bufferTo=<optimized out>, doBuffer=true) at items/qquickgridview.cpp:520
#22 0x00007f9e061a5ec2 in QQuickItemViewPrivate::refill(double, double) (this=0x55d572965580, from=-0, to=588) at items/qquickitemview.cpp:1814
#23 0x00007f9e061a8b03 in QQuickItemViewPrivate::layout() (this=0x55d572965580) at items/qquickitemview.cpp:1920
#24 0x00007f9e060f7e5a in QQuickWindowPrivate::polishItems() (this=this@entry=0x55d572701c00) at items/qquickwindow.cpp:393
#25 0x00007f9e06184692 in QQuickRenderControl::polishItems() (this=<optimized out>) at items/qquickrendercontrol.cpp:277
#26 0x00007f9e06449169 in QQuickWidgetPrivate::render(bool) (this=0x55d572711070, needsSync=<optimized out>) at qquickwidget.cpp:306
#27 0x00007f9e064493d6 in QQuickWidgetPrivate::renderSceneGraph() (this=0x55d572711070) at qquickwidget.cpp:361
#28 0x00007f9e07f04ad5 in QObject::event(QEvent*) (this=0x55d572d79da0, e=0x7ffe039431d0) at kernel/qobject.cpp:1369
#29 0x00007f9e08aadd02 in QApplicationPrivate::notify_helper(QObject*, QEvent*) () at /lib64/libQt5Widgets.so.5
#30 0x00007f9e07eda1c8 in QCoreApplication::notifyInternal2(QObject*, QEvent*) (receiver=0x55d572d79da0, event=0x7ffe039431d0) at kernel/qcoreapplication.cpp:1064
#31 0x00007f9e07f2a3b1 in QTimerInfoList::activateTimers() (this=0x55d571d24930) at kernel/qtimerinfo_unix.cpp:643
#32 0x00007f9e07f2acd4 in timerSourceDispatch (source=<optimized out>) at kernel/qeventdispatcher_glib.cpp:183
#33 idleTimerSourceDispatch(GSource*, GSourceFunc, gpointer) (source=<optimized out>) at kernel/qeventdispatcher_glib.cpp:230
#34 0x00007f9e064a9faf in g_main_dispatch (context=0x7f9df0005010) at ../glib/gmain.c:3417
#35 g_main_context_dispatch (context=0x7f9df0005010) at ../glib/gmain.c:4135
#36 0x00007f9e064ff2c8 in g_main_context_iterate.constprop.0 (context=context@entry=0x7f9df0005010, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>) at ../glib/gmain.c:4211
#37 0x00007f9e064a7940 in g_main_context_iteration (context=0x7f9df0005010, may_block=1) at ../glib/gmain.c:4276
#38 0x00007f9e07f2b02a in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) (this=0x55d571d2cfd0, flags=...) at kernel/qeventdispatcher_glib.cpp:423
#39 0x00007f9e07ed8c1a in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) (this=this@entry=0x7ffe03943470, flags=..., flags@entry=...) at ../../include/QtCore/../../src/corelib/global/qflags.h:69
#40 0x00007f9e07ee0ce2 in QCoreApplication::exec() () at ../../include/QtCore/../../src/corelib/global/qflags.h:121
#41 0x000055d570c430c3 in main ()
[Inferior 1 (process 23112) detached]

#13 0x00007f9dac2cfb50 in QGtk2StylePlugin::create(QString const&) () at /usr/lib64/qt5/plugins/styles/libqgtk2style.so

crash is in an unsupported style

Yeah, that was it, thank you. 

If anyone else stumbles upon this issue, for me it was fixed by running `dnf remove qt5-qtstyleplugins`

Created attachment 153175 [details]
New crash information added by DrKonqi

systemsettings (5.26.1) using Qt 5.15.6

Instalacion fresca de KDE Neon. Primer inicio. Trate de entrar a la configuracion de aspecto y Preferencias del sistema se cerro.

-- Backtrace (Reduced):
#4  __pthread_kill_implementation (no_tid=0, signo=6, threadid=139929861834304) at ./nptl/pthread_kill.c:44
#5  __pthread_kill_internal (signo=6, threadid=139929861834304) at ./nptl/pthread_kill.c:78
#6  __GI___pthread_kill (threadid=139929861834304, signo=signo@entry=6) at ./nptl/pthread_kill.c:89
#7  0x00007f43fbf20476 in __GI_raise (sig=sig@entry=6) at ../sysdeps/posix/raise.c:26
#8  0x00007f43fbf067f3 in __GI_abort () at ./stdlib/abort.c:79