I now boot into a snapshot that was made prior to the last stable update from last year with kernel 5.9. There was no error like now.
Application: Dolphin (dolphin), signal: Segmentation fault
[KCrash Handler]
#4 0x00007fcd9712e8e5 in QAction::setEnabled(bool) () from /usr/lib/libQt5Widgets.so.5
#5 0x00007fcd966a1dd6 in ?? () from /usr/lib/libQt5Core.so.5
#6 0x00007fcd97223d53 in QAbstractButton::clicked(bool) () from /usr/lib/libQt5Widgets.so.5
#7 0x00007fcd972246dc in ?? () from /usr/lib/libQt5Widgets.so.5
#8 0x00007fcd97226083 in ?? () from /usr/lib/libQt5Widgets.so.5
#9 0x00007fcd97226263 in QAbstractButton::mouseReleaseEvent(QMouseEvent*) () from /usr/lib/libQt5Widgets.so.5
#10 0x00007fcd97173b0e in QWidget::event(QEvent*) () from /usr/lib/libQt5Widgets.so.5
#11 0x00007fcd97132752 in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/libQt5Widgets.so.5
#12 0x00007fcd9713987b in QApplication::notify(QObject*, QEvent*) () from /usr/lib/libQt5Widgets.so.5
#13 0x00007fcd9666aa7a in QCoreApplication::notifyInternal2(QObject*, QEvent*) () from /usr/lib/libQt5Core.so.5
#14 0x00007fcd9713887e in QApplicationPrivate::sendMouseEvent(QWidget*, QMouseEvent*, QWidget*, QWidget*, QWidget**, QPointer<QWidget>&, bool, bool) () from /usr/lib/libQt5Widgets.so.5
#15 0x00007fcd9718c249 in ?? () from /usr/lib/libQt5Widgets.so.5
#16 0x00007fcd9718f63f in ?? () from /usr/lib/libQt5Widgets.so.5
#17 0x00007fcd97132752 in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/libQt5Widgets.so.5
#18 0x00007fcd9666aa7a in QCoreApplication::notifyInternal2(QObject*, QEvent*) () from /usr/lib/libQt5Core.so.5
#19 0x00007fcd96a44594 in QGuiApplicationPrivate::processMouseEvent(QWindowSystemInterfacePrivate::MouseEvent*) () from /usr/lib/libQt5Gui.so.5
#20 0x00007fcd96a19bb5 in QWindowSystemInterface::sendWindowSystemEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Gui.so.5
#21 0x00007fcd9104316c in ?? () from /usr/lib/libQt5XcbQpa.so.5
#22 0x00007fcd9450ba84 in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#23 0x00007fcd9455f9b1 in ?? () from /usr/lib/libglib-2.0.so.0
#24 0x00007fcd9450a2b1 in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#25 0x00007fcd966c36e1 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5
#26 0x00007fcd966693fc in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5
#27 0x00007fcd9733620a in QDialog::exec() () from /usr/lib/libQt5Widgets.so.5
#28 0x00007fcd98259603 in KIO::JobUiDelegate::askFileRename(KJob*, QString const&, QUrl const&, QUrl const&, QFlags<KIO::RenameDialog_Option>, QString&, unsigned long long, unsigned long long, QDateTime const&, QDateTime const&, QDateTime const&, QDateTime const&) () from /usr/lib/libKF5KIOWidgets.so.5
#29 0x00007fcd97fc052d in ?? () from /usr/lib/libKF5KIOCore.so.5
#30 0x00007fcd966a1dd6 in ?? () from /usr/lib/libQt5Core.so.5
#31 0x00007fcd9785f51d in KJob::result(KJob*, KJob::QPrivateSignal) () from /usr/lib/libKF5CoreAddons.so.5
#32 0x00007fcd9786005c in KJob::finishJob(bool) () from /usr/lib/libKF5CoreAddons.so.5
#33 0x00007fcd966a1dd6 in ?? () from /usr/lib/libQt5Core.so.5
#34 0x00007fcd97fe05e6 in KIO::SlaveInterface::dispatch(int, QByteArray const&) () from /usr/lib/libKF5KIOCore.so.5
#35 0x00007fcd97fded4a in KIO::SlaveInterface::dispatch() () from /usr/lib/libKF5KIOCore.so.5
#36 0x00007fcd97fe284b in KIO::Slave::gotInput() () from /usr/lib/libKF5KIOCore.so.5
#37 0x00007fcd966a1dd6 in ?? () from /usr/lib/libQt5Core.so.5
#38 0x00007fcd96697582 in QObject::event(QEvent*) () from /usr/lib/libQt5Core.so.5
#39 0x00007fcd97132752 in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/libQt5Widgets.so.5
#40 0x00007fcd9666aa7a in QCoreApplication::notifyInternal2(QObject*, QEvent*) () from /usr/lib/libQt5Core.so.5
#41 0x00007fcd9666d573 in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) () from /usr/lib/libQt5Core.so.5
#42 0x00007fcd966c40a4 in ?? () from /usr/lib/libQt5Core.so.5
#43 0x00007fcd9450ba84 in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#44 0x00007fcd9455f9b1 in ?? () from /usr/lib/libglib-2.0.so.0
#45 0x00007fcd9450a2b1 in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#46 0x00007fcd966c36e1 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5
#47 0x00007fcd966693fc in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5
#48 0x00007fcd96671894 in QCoreApplication::exec() () from /usr/lib/libQt5Core.so.5
#49 0x00007fcd98804f43 in kdemain () from /usr/lib/libkdeinit5_dolphin.so
#50 0x00007fcd9861c152 in __libc_start_main () from /usr/lib/libc.so.6
#51 0x00005612b089905e in _start ()
[Inferior 1 (process 8906) detached]