SUMMARY
On Wayland session, I opened Window Behavior KCM in System Settings and clicked
on "Titlebar Actions" tab. Under "Titlebar and Frame Actions", I chose "Close"
option to Active/Middle click combobox, then I clicked on "Apply" button and
System Settings crashed.

Application: System Settings (systemsettings5), signal: Segmentation fault
Content of s_kcrashErrorMessage: [Current thread is 1 (Thread 0x7f8332be68c0 (LWP 10453))]
[New LWP 10474]
[New LWP 10475]
[New LWP 10476]
[New LWP 10477]
[New LWP 10478]
[New LWP 10479]
[New LWP 10480]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
0x00007f8336e1faff in __GI___poll (fds=fds@entry=0x7ffe0af50ca8, nfds=nfds@entry=1, timeout=timeout@entry=1000) at ../sysdeps/unix/sysv/linux/poll.c:29

Thread 8 (Thread 0x7f8319f76700 (LWP 10480)):
#0  __GI___libc_read (nbytes=16, buf=0x7f8319f75ab0, fd=15) at ../sysdeps/unix/sysv/linux/read.c:26
#1  __GI___libc_read (fd=15, buf=buf@entry=0x7f8319f75ab0, nbytes=nbytes@entry=16) at ../sysdeps/unix/sysv/linux/read.c:24
#2  0x00007f83350f389f in read (__nbytes=16, __buf=0x7f8319f75ab0, __fd=<optimized out>) at /usr/include/x86_64-linux-gnu/bits/unistd.h:44
#3  g_wakeup_acknowledge (wakeup=0x7f83100039a0) at ../../../glib/gwakeup.c:210
#4  0x00007f83350aacde in g_main_context_check (context=context@entry=0x7f8308000c20, max_priority=2147483647, fds=fds@entry=0x7f8308004a60, n_fds=n_fds@entry=1) at ../../../glib/gmain.c:3825
#5  0x00007f83350ab132 in g_main_context_iterate (context=context@entry=0x7f8308000c20, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>) at ../../../glib/gmain.c:4044
#6  0x00007f83350ab2c3 in g_main_context_iteration (context=0x7f8308000c20, may_block=may_block@entry=1) at ../../../glib/gmain.c:4108
#7  0x00007f8337539fbb in QEventDispatcherGlib::processEvents (this=0x7f8308000b60, flags=...) at kernel/qeventdispatcher_glib.cpp:425
#8  0x00007f83374de1ab in QEventLoop::exec (this=this@entry=0x7f8319f75cc0, flags=..., flags@entry=...) at ../../include/QtCore/../../src/corelib/global/qflags.h:141
#9  0x00007f83372f8a12 in QThread::exec (this=this@entry=0x55748d9924d0) at ../../include/QtCore/../../src/corelib/global/qflags.h:121
#10 0x00007f83365edfa9 in QQmlThreadPrivate::run (this=0x55748d9924d0) at qml/ftw/qqmlthread.cpp:155
#11 0x00007f83372f9bac in QThreadPrivate::start (arg=0x55748d9924d0) at thread/qthread_unix.cpp:329
#12 0x00007f83359bb609 in start_thread (arg=<optimized out>) at pthread_create.c:477
#13 0x00007f8336e2c293 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

Thread 7 (Thread 0x7f8329630700 (LWP 10479)):
#0  0x00007f8336e1faff in __GI___poll (fds=0x7f8310004e60, nfds=1, timeout=-1) at ../sysdeps/unix/sysv/linux/poll.c:29
#1  0x00007f83350ab18e in g_main_context_poll (priority=<optimized out>, n_fds=1, fds=0x7f8310004e60, timeout=<optimized out>, context=0x7f8310000c20) at ../../../glib/gmain.c:4346
#2  g_main_context_iterate (context=context@entry=0x7f8310000c20, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>) at ../../../glib/gmain.c:4042
#3  0x00007f83350ab2c3 in g_main_context_iteration (context=0x7f8310000c20, may_block=may_block@entry=1) at ../../../glib/gmain.c:4108
#4  0x00007f8337539fbb in QEventDispatcherGlib::processEvents (this=0x7f8310000b60, flags=...) at kernel/qeventdispatcher_glib.cpp:425
#5  0x00007f83374de1ab in QEventLoop::exec (this=this@entry=0x7f832962fcc0, flags=..., flags@entry=...) at ../../include/QtCore/../../src/corelib/global/qflags.h:141
#6  0x00007f83372f8a12 in QThread::exec (this=this@entry=0x55748d6d5eb0) at ../../include/QtCore/../../src/corelib/global/qflags.h:121
#7  0x00007f83365edfa9 in QQmlThreadPrivate::run (this=0x55748d6d5eb0) at qml/ftw/qqmlthread.cpp:155
#8  0x00007f83372f9bac in QThreadPrivate::start (arg=0x55748d6d5eb0) at thread/qthread_unix.cpp:329
#9  0x00007f83359bb609 in start_thread (arg=<optimized out>) at pthread_create.c:477
#10 0x00007f8336e2c293 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

Thread 6 (Thread 0x7f832a1ba700 (LWP 10478)):
#0  futex_wait_cancelable (private=<optimized out>, expected=0, futex_word=0x55748d326c7c) at ../sysdeps/nptl/futex-internal.h:183
#1  __pthread_cond_wait_common (abstime=0x0, clockid=0, mutex=0x55748d326c28, cond=0x55748d326c50) at pthread_cond_wait.c:508
#2  __pthread_cond_wait (cond=0x55748d326c50, mutex=0x55748d326c28) at pthread_cond_wait.c:638
#3  0x00007f832b717e6b in ?? () from /usr/lib/x86_64-linux-gnu/dri/i965_dri.so
#4  0x00007f832b717a6b in ?? () from /usr/lib/x86_64-linux-gnu/dri/i965_dri.so
#5  0x00007f83359bb609 in start_thread (arg=<optimized out>) at pthread_create.c:477
#6  0x00007f8336e2c293 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

Thread 5 (Thread 0x7f832a9bb700 (LWP 10477)):
#0  futex_wait_cancelable (private=<optimized out>, expected=0, futex_word=0x55748d326c78) at ../sysdeps/nptl/futex-internal.h:183
#1  __pthread_cond_wait_common (abstime=0x0, clockid=0, mutex=0x55748d326c28, cond=0x55748d326c50) at pthread_cond_wait.c:508
#2  __pthread_cond_wait (cond=0x55748d326c50, mutex=0x55748d326c28) at pthread_cond_wait.c:638
#3  0x00007f832b717e6b in ?? () from /usr/lib/x86_64-linux-gnu/dri/i965_dri.so
#4  0x00007f832b717a6b in ?? () from /usr/lib/x86_64-linux-gnu/dri/i965_dri.so
#5  0x00007f83359bb609 in start_thread (arg=<optimized out>) at pthread_create.c:477
#6  0x00007f8336e2c293 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

Thread 4 (Thread 0x7f832b1bc700 (LWP 10476)):
#0  futex_wait_cancelable (private=<optimized out>, expected=0, futex_word=0x55748d326c78) at ../sysdeps/nptl/futex-internal.h:183
#1  __pthread_cond_wait_common (abstime=0x0, clockid=0, mutex=0x55748d326c28, cond=0x55748d326c50) at pthread_cond_wait.c:508
#2  __pthread_cond_wait (cond=0x55748d326c50, mutex=0x55748d326c28) at pthread_cond_wait.c:638
#3  0x00007f832b717e6b in ?? () from /usr/lib/x86_64-linux-gnu/dri/i965_dri.so
#4  0x00007f832b717a6b in ?? () from /usr/lib/x86_64-linux-gnu/dri/i965_dri.so
#5  0x00007f83359bb609 in start_thread (arg=<optimized out>) at pthread_create.c:477
#6  0x00007f8336e2c293 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

Thread 3 (Thread 0x7f833086e700 (LWP 10475)):
#0  futex_wait_cancelable (private=<optimized out>, expected=0, futex_word=0x55748d326c78) at ../sysdeps/nptl/futex-internal.h:183
#1  __pthread_cond_wait_common (abstime=0x0, clockid=0, mutex=0x55748d326c28, cond=0x55748d326c50) at pthread_cond_wait.c:508
#2  __pthread_cond_wait (cond=0x55748d326c50, mutex=0x55748d326c28) at pthread_cond_wait.c:638
#3  0x00007f832b717e6b in ?? () from /usr/lib/x86_64-linux-gnu/dri/i965_dri.so
#4  0x00007f832b717a6b in ?? () from /usr/lib/x86_64-linux-gnu/dri/i965_dri.so
#5  0x00007f83359bb609 in start_thread (arg=<optimized out>) at pthread_create.c:477
#6  0x00007f8336e2c293 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

Thread 2 (Thread 0x7f8331f7a700 (LWP 10474)):
#0  0x00007f8336e1faff in __GI___poll (fds=0x7f832c005240, nfds=1, timeout=-1) at ../sysdeps/unix/sysv/linux/poll.c:29
#1  0x00007f83350ab18e in g_main_context_poll (priority=<optimized out>, n_fds=1, fds=0x7f832c005240, timeout=<optimized out>, context=0x7f832c000c20) at ../../../glib/gmain.c:4346
#2  g_main_context_iterate (context=context@entry=0x7f832c000c20, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>) at ../../../glib/gmain.c:4042
#3  0x00007f83350ab2c3 in g_main_context_iteration (context=0x7f832c000c20, may_block=may_block@entry=1) at ../../../glib/gmain.c:4108
#4  0x00007f8337539fbb in QEventDispatcherGlib::processEvents (this=0x7f832c000b60, flags=...) at kernel/qeventdispatcher_glib.cpp:425
#5  0x00007f83374de1ab in QEventLoop::exec (this=this@entry=0x7f8331f79cb0, flags=..., flags@entry=...) at ../../include/QtCore/../../src/corelib/global/qflags.h:141
#6  0x00007f83372f8a12 in QThread::exec (this=this@entry=0x7f833628dd80 <(anonymous namespace)::Q_QGS__q_manager::innerFunction()::holder>) at ../../include/QtCore/../../src/corelib/global/qflags.h:121
#7  0x00007f8336209f4b in QDBusConnectionManager::run (this=0x7f833628dd80 <(anonymous namespace)::Q_QGS__q_manager::innerFunction()::holder>) at qdbusconnection.cpp:179
#8  0x00007f83372f9bac in QThreadPrivate::start (arg=0x7f833628dd80 <(anonymous namespace)::Q_QGS__q_manager::innerFunction()::holder>) at thread/qthread_unix.cpp:329
#9  0x00007f83359bb609 in start_thread (arg=<optimized out>) at pthread_create.c:477
#10 0x00007f8336e2c293 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

Thread 1 (Thread 0x7f8332be68c0 (LWP 10453)):
[KCrash Handler]
#6  0x00007f8334f8b794 in QWaylandClientExtensionPrivate::handleRegistryGlobal (data=0x557498fad230, registry=0x55748d11ee40, id=45, interface=..., version=1) at global/qwaylandclientextension.cpp:67
#7  0x00007f8334f67822 in QtWaylandClient::QWaylandDisplay::registry_global (this=<optimized out>, id=45, interface=..., version=1) at qwaylanddisplay.cpp:396
#8  0x00007f8334f95d16 in QtWayland::wl_registry::handle_global (data=0x55748d122970, object=<optimized out>, name=45, interface=0x5574a0035710 "org_kde_kwin_blur_manager", version=1) at /usr/include/x86_64-linux-gnu/qt5/QtCore/qarraydata.h:236
#9  0x00007f8332fb3ff5 in ffi_call_unix64 () at ../src/x86/unix64.S:101
#10 0x00007f8332fb340a in ffi_call_int (cif=<optimized out>, fn=<optimized out>, rvalue=<optimized out>, avalue=<optimized out>, closure=<optimized out>) at ../src/x86/ffi64.c:669
#11 0x00007f8334ee33a8 in wl_closure_invoke (closure=0x5574a0035630, flags=1, target=<optimized out>, opcode=0, data=<optimized out>) at ../src/connection.c:1018
#12 0x00007f8334edfc48 in dispatch_event (display=display@entry=0x55748d122ea0, queue=<optimized out>) at ../src/wayland-client.c:1445
#13 0x00007f8334ee121c in dispatch_queue (queue=0x55748d122f70, display=0x55748d122ea0) at ../src/wayland-client.c:1591
#14 wl_display_dispatch_queue_pending (display=0x55748d122ea0, queue=0x55748d122f70) at ../src/wayland-client.c:1833
#15 0x00007f8334ee1280 in wl_display_dispatch_pending (display=<optimized out>) at ../src/wayland-client.c:1896
#16 0x00007f8334f67155 in QtWaylandClient::QWaylandDisplay::flushRequests (this=0x55748d122960) at qwaylanddisplay.cpp:221
#17 0x00007f83375166f0 in doActivate<false> (sender=0x55748d15b2e0, signal_index=3, argv=0x7ffe0af51a90) at ../../include/QtCore/../../src/corelib/kernel/qobjectdefs_impl.h:395
#18 0x00007f833750fa87 in QMetaObject::activate (sender=sender@entry=0x55748d15b2e0, m=m@entry=0x7f8337779b60 <QSocketNotifier::staticMetaObject>, local_signal_index=local_signal_index@entry=0, argv=argv@entry=0x7ffe0af51a90) at kernel/qobject.cpp:3946
#19 0x00007f833751a733 in QSocketNotifier::activated (this=this@entry=0x55748d15b2e0, _t1=..., _t2=<optimized out>, _t3=...) at .moc/moc_qsocketnotifier.cpp:178
#20 0x00007f833751aed3 in QSocketNotifier::event (this=0x55748d15b2e0, e=0x7ffe0af51d60) at kernel/qsocketnotifier.cpp:302
#21 0x00007f83380dfdc3 in QApplicationPrivate::notify_helper (this=this@entry=0x55748d11c3a0, receiver=receiver@entry=0x55748d15b2e0, e=e@entry=0x7ffe0af51d60) at kernel/qapplication.cpp:3632
#22 0x00007f83380e8bb8 in QApplication::notify (this=0x7ffe0af52090, receiver=0x55748d15b2e0, e=0x7ffe0af51d60) at kernel/qapplication.cpp:3156
#23 0x00007f83374df69a in QCoreApplication::notifyInternal2 (receiver=0x55748d15b2e0, event=0x7ffe0af51d60) at ../../include/QtCore/5.15.2/QtCore/private/../../../../../src/corelib/thread/qthread_p.h:325
#24 0x00007f833753aba5 in socketNotifierSourceDispatch (source=0x55748d15b440) at kernel/qeventdispatcher_glib.cpp:107
#25 0x00007f83350aaf9d in g_main_dispatch (context=0x55748d13a270) at ../../../glib/gmain.c:3309
#26 g_main_context_dispatch (context=context@entry=0x55748d13a270) at ../../../glib/gmain.c:3974
#27 0x00007f83350ab220 in g_main_context_iterate (context=context@entry=0x55748d13a270, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>) at ../../../glib/gmain.c:4047
#28 0x00007f83350ab2c3 in g_main_context_iteration (context=0x55748d13a270, may_block=may_block@entry=1) at ../../../glib/gmain.c:4108
#29 0x00007f8337539fa2 in QEventDispatcherGlib::processEvents (this=0x55748d15b2c0, flags=...) at kernel/qeventdispatcher_glib.cpp:423
#30 0x00007f83374de1ab in QEventLoop::exec (this=this@entry=0x7ffe0af51f70, flags=..., flags@entry=...) at ../../include/QtCore/../../src/corelib/global/qflags.h:141
#31 0x00007f83374e6354 in QCoreApplication::exec () at ../../include/QtCore/../../src/corelib/global/qflags.h:121
#32 0x000055748b105392 in main (argc=<optimized out>, argv=<optimized out>) at ./app/main.cpp:222
[Inferior 1 (process 10453) detached]