When I disable my laptop screen (with a VGA monitor attached, enabled, and set as primary output) through the kscreen kcm, the kwin_wayland process crashes with this stacktrace:

Core was generated by `/usr/bin/kwin_wayland --xwayland --libinput --exit-with-session=/usr/lib/startp'.
Program terminated with signal SIGABRT, Aborted.
#0  0x00007f3df4ab3860 in raise () from /usr/lib/libc.so.6
[Current thread is 1 (Thread 0x7f3df7f226c0 (LWP 1294))]
(gdb) bt
#0  0x00007f3df4ab3860 in raise () at /usr/lib/libc.so.6
#1  0x00007f3df4ab4e48 in abort () at /usr/lib/libc.so.6
#2  0x00007f3df4ec4d57 in __gnu_cxx::__verbose_terminate_handler() () at /build/gcc/src/gcc/libstdc++-v3/libsupc++/vterminate.cc:95
#3  0x00007f3df4ec28c6 in __cxxabiv1::__terminate(void (*)()) (handler=<optimized out>) at /build/gcc/src/gcc/libstdc++-v3/libsupc++/eh_terminate.cc:47
#4  0x00007f3df4ec179a in __cxa_call_terminate(_Unwind_Exception*) (ue_header=ue_header@entry=0x557fdfccfad0) at /build/gcc/src/gcc/libstdc++-v3/libsupc++/eh_call.cc:54
#5  0x00007f3df4ec2189 in __cxxabiv1::__gxx_personality_v0(int, _Unwind_Action, _Unwind_Exception_Class, _Unwind_Exception*, _Unwind_Context*) (version=<optimized out>, actions=<optimized out>, exception_class=5138137972254386944, ue_header=0x557fdfccfad0, context=<optimized out>) at /build/gcc/src/gcc/libstdc++-v3/libsupc++/eh_personality.cc:676
#6  0x00007f3ded5f2ca3 in _Unwind_RaiseException_Phase2 (exc=exc@entry=0x557fdfccfad0, context=context@entry=0x7ffef10008e0) at /build/gcc/src/gcc/libgcc/unwind.inc:62
#7  0x00007f3ded5f34ce in _Unwind_Resume (exc=0x557fdfccfad0) at /build/gcc/src/gcc/libgcc/unwind.inc:230
#8  0x00007f3df5685992 in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) () at /usr/lib/libQt5Core.so.5
#9  0x00007f3df56dbe36 in QEventDispatcherUNIX::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib/libQt5Core.so.5
#10 0x00007f3ddf5945de in QUnixEventDispatcherQPA::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib/qt/plugins/platforms/KWinQpaPlugin.so
#11 0x00007f3ddc9de31b in KWin::DrmBackend::~DrmBackend() (this=0x557fdfd0eb30, __in_chrg=<optimized out>) at /home/pieter/builds/kwin/src/kwin-5.12.0/plugins/platforms/drm/drm_backend.cpp:91
#12 0x00007f3ddc9de67a in KWin::DrmBackend::~DrmBackend() (this=0x557fdfd0eb30, __in_chrg=<optimized out>) at /home/pieter/builds/kwin/src/kwin-5.12.0/plugins/platforms/drm/drm_backend.cpp:99
#13 0x00007f3df56774f7 in  () at /usr/lib/libQt5Core.so.5
#14 0x00007f3df56799c6 in  () at /usr/lib/libQt5Core.so.5
#15 0x00007f3df4ab67b2 in __cxa_finalize () at /usr/lib/libc.so.6
#16 0x00007f3df5465034 in  () at /usr/lib/libQt5Core.so.5
#17 0x00007ffef1001470 in  ()
#18 0x00007f3df7da7af3 in _dl_fini () at /lib64/ld-linux-x86-64.so.2

I am using kwin 5.12.0, rebuilt locally using the Arch PKGBUILD to add debug symbols (I can do the same with Qt if needed, I am using 5.10.0).
Attached also the output of `qdbus org.kde.KWin /KWin supportInformation` - please let me know if you need any more information.
Thanks in advance!