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of Fedora, you are encouraged  change the 'version' to a later Fedora 
version prior this bug is closed as described in the policy above.

Although we aim to fix as many bugs as possible during every release's 
lifetime, sometimes those efforts are overtaken by events. Often a 
more recent Fedora release includes newer upstream software that fixes 
bugs or makes them obsolete.

This message is a reminder that Fedora 33 is nearing its end of life.
Fedora will stop maintaining and issuing updates for Fedora 33 on 2021-11-30.
It is Fedora's policy to close all bug reports from releases that are no longer
maintained. At that time this bug will be closed as EOL if it remains open with a
Fedora 'version' of '33'.

Package Maintainer: If you wish for this bug to remain open because you
plan to fix it in a currently maintained version, simply change the 'version' 
to a later Fedora version.

Thank you for reporting this issue and we are sorry that we were not 
able to fix it before Fedora 33 is end of life. If you would still like 
to see this bug fixed and are able to reproduce it against a later version 
of Fedora, you are encouraged  change the 'version' to a later Fedora 
version prior this bug is closed as described in the policy above.

Although we aim to fix as many bugs as possible during every release's 
lifetime, sometimes those efforts are overtaken by events. Often a 
more recent Fedora release includes newer upstream software that fixes 
bugs or makes them obsolete.

This message is a reminder that Fedora 33 is nearing its end of life.
Fedora will stop maintaining and issuing updates for Fedora 33 on 2021-11-30.
It is Fedora's policy to close all bug reports from releases that are no longer
maintained. At that time this bug will be closed as EOL if it remains open with a
Fedora 'version' of '33'.

Package Maintainer: If you wish for this bug to remain open because you
plan to fix it in a currently maintained version, simply change the 'version' 
to a later Fedora version.

Thank you for reporting this issue and we are sorry that we were not 
able to fix it before Fedora 33 is end of life. If you would still like 
to see this bug fixed and are able to reproduce it against a later version 
of Fedora, you are encouraged  change the 'version' to a later Fedora 
version prior this bug is closed as described in the policy above.

Although we aim to fix as many bugs as possible during every release's 
lifetime, sometimes those efforts are overtaken by events. Often a 
more recent Fedora release includes newer upstream software that fixes 
bugs or makes them obsolete.

It's still segfaulting on Fedora 35.

(i.e. both the client and server are on Fedora 35)

Client output:

$ x2goclient                              
QSocketNotifier: Can only be used with threads started with QThread
x2go-INFO-1> "Starting X2Go Client 4.1.2.2..."
x2go-WARNING-1> English language requested, not loading translator.
x2go-WARNING-1> English language requested, not loading translator.
x2go-INFO-3> "Started X2Go Client."
x2go-INFO-8> "Starting connection to server: hostb.example.org:22"
RESUMING SESSION is KDRIVE:  false
zsh: segmentation fault (core dumped)  x2goclient
WARNING: failed to kill process group '3858': No such process


Version: 
x2goclient-4.1.2.2-5.fc35.x86_64

Current stack trace:
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x00007fdb70fbfcd6 in XDefaultRootWindow (dpy=0x55f9e57ae440) at /usr/src/debug/libX11-1.7.2-3.fc35.x86_64/src/Macros.c:52
52	    return (RootWindow(dpy,DefaultScreen(dpy)));
[Current thread is 1 (Thread 0x7fdb6bda0b40 (LWP 3858))]
(gdb) bt
#0  0x00007fdb70fbfcd6 in XDefaultRootWindow (dpy=0x55f9e57ae440) at /usr/src/debug/libX11-1.7.2-3.fc35.x86_64/src/Macros.c:52
#1  0x000055f9e3e43bcd in ONMainWindow::X11FindWindow(QString, long) [clone .isra.0] (text=..., rootWin=0, this=<optimized out>) at ../src/onmainwindow.cpp:13240
#2  0x000055f9e3dc385e in ONMainWindow::findWindow(QString) (this=0x55f9e58b9c10, text=...) at ../src/onmainwindow.cpp:13273
#3  ONMainWindow::slotFindProxyWin() (this=0x55f9e58b9c10) at ../src/onmainwindow.cpp:11654
#4  0x00007fdb6fceb3f0 in doActivate<false>(QObject*, int, void**) (sender=0x55f9e5b71810, signal_index=3, argv=0x7fff99b4d940) at kernel/qobject.cpp:3898
#5  0x00007fdb6fce6327 in QMetaObject::activate(QObject*, QMetaObject const*, int, void**)
    (sender=<optimized out>, m=m@entry=0x7fdb6ff905a0 <QTimer::staticMetaObject>, local_signal_index=local_signal_index@entry=0, argv=argv@entry=0x7fff99b4d940)
    at kernel/qobject.cpp:3946
#6  0x00007fdb6fcee64e in QTimer::timeout(QTimer::QPrivateSignal) (this=<optimized out>, _t1=...) at .moc/moc_qtimer.cpp:205
#7  0x00007fdb6fce1e9f in QObject::event(QEvent*) (this=0x55f9e5b71810, e=0x7fff99b4daa0) at kernel/qobject.cpp:1336
#8  0x00007fdb7094b443 in QApplicationPrivate::notify_helper(QObject*, QEvent*) (this=<optimized out>, receiver=0x55f9e5b71810, e=0x7fff99b4daa0) at kernel/qapplication.cpp:3632
#9  0x00007fdb6fcb7798 in QCoreApplication::notifyInternal2(QObject*, QEvent*) (receiver=0x55f9e5b71810, event=0x7fff99b4daa0) at kernel/qcoreapplication.cpp:1064
#10 0x00007fdb6fd07e63 in QTimerInfoList::activateTimers() (this=0x55f9e58e0360) at kernel/qtimerinfo_unix.cpp:643
#11 0x00007fdb6fd087b4 in timerSourceDispatch (source=<optimized out>) at kernel/qeventdispatcher_glib.cpp:183
#12 idleTimerSourceDispatch(GSource*, GSourceFunc, gpointer) (source=<optimized out>) at kernel/qeventdispatcher_glib.cpp:230
#13 0x00007fdb6e56833f in g_main_dispatch (context=0x7fdb64005000) at ../glib/gmain.c:3381
#14 g_main_context_dispatch (context=0x7fdb64005000) at ../glib/gmain.c:4099
#15 0x00007fdb6e5bd2b8 in g_main_context_iterate.constprop.0 (context=context@entry=0x7fdb64005000, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>)
    at ../glib/gmain.c:4175
#16 0x00007fdb6e5659e3 in g_main_context_iteration (context=0x7fdb64005000, may_block=1) at ../glib/gmain.c:4240
#17 0x00007fdb6fd08b78 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) (this=0x55f9e59672b0, flags=...) at kernel/qeventdispatcher_glib.cpp:423
#18 0x00007fdb6fcb61a2 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) (this=this@entry=0x7fff99b4dd40, flags=..., flags@entry=...)
    at ../../include/QtCore/../../src/corelib/global/qflags.h:69
#19 0x00007fdb6fcbe6e4 in QCoreApplication::exec() () at ../../include/QtCore/../../src/corelib/global/qflags.h:121
#20 0x00007fdb702b5c50 in QGuiApplication::exec() () at kernel/qguiapplication.cpp:1860
#21 0x00007fdb7094b3b9 in QApplication::exec() () at kernel/qapplication.cpp:2824
#22 0x000055f9e3df786f in x2goMain(int, char**) (argc=<optimized out>, argv=<optimized out>) at ../src/ongetpass.cpp:114
#23 0x000055f9e3d73a2a in wrap_x2go_main(int, char**) (argv=0x7fff99b4e258, argc=1) at ../src/x2goclient.cpp:36
#24 fork_helper(int, char**) (argv=<optimized out>, argc=<optimized out>) at ../src/x2goclient.cpp:89
#25 main(int, char**) (argc=1, argv=0x7fff99b4e258) at ../src/x2goclient.cpp:175

Try running:

env QT_QPA_PLATFORM=xcb x2goclient

does that help?

Yes, using `QT_QPA_PLATFORM=xcb x2goclient` does help.

With that I get a usable session where xclock, xterm and wireshark pretty much work as expected.

There is some noise with wireshark, though, e.g. on the console it reads:

11:54:31.422     Main Warn X server does not support XInput 2
11:54:31.832     Main Warn QXcbConnection: Failed to initialize GLX
11:54:32.513     Main Warn QXcbConnection: XCB error: 1 (BadRequest), sequence: 169, resource id: 233, major code: 130 (Unknown), minor code: 4

And gnome-shell basically complains on each key press like this:

Nov 12 11:58:56 example.org gnome-shell[1833]: Window manager warning: last_user_time (332196370) is greater than comparison timestamp (96600390).  This most likely represents a buggy client sending inaccurate timestamps in messages such as _NET_ACTIVE_WINDOW.  Trying to work around...
Nov 12 11:58:56 example.org gnome-shell[1833]: Window manager warning: 0x1a00121 appears to be one of the offending windows with a timestamp of 332196370.  Working around...

However, at least keyboard input is usable inside wireshark.

This message is a reminder that Fedora Linux 35 is nearing its end of life.
Fedora will stop maintaining and issuing updates for Fedora Linux 35 on 2022-12-13.
It is Fedora's policy to close all bug reports from releases that are no longer
maintained. At that time this bug will be closed as EOL if it remains open with a
'version' of '35'.

Package Maintainer: If you wish for this bug to remain open because you
plan to fix it in a currently maintained version, change the 'version' 
to a later Fedora Linux version.

Thank you for reporting this issue and we are sorry that we were not 
able to fix it before Fedora Linux 35 is end of life. If you would still like 
to see this bug fixed and are able to reproduce it against a later version 
of Fedora Linux, you are encouraged to change the 'version' to a later version
prior to this bug being closed.

Fedora Linux 35 entered end-of-life (EOL) status on 2022-12-13.

Fedora Linux 35 is no longer maintained, which means that it
will not receive any further security or bug fix updates. As a result we
are closing this bug.

If you can reproduce this bug against a currently maintained version of Fedora Linux
please feel free to reopen this bug against that version. Note that the version
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Thank you for reporting this bug and we are sorry it could not be fixed.