Hallo Knut, there is still the shadow that this issue might be first sent to the people from BunsenLabs.
Nevertheless from looking at the stack it looks like a Qt5 application but we end up here in some Gtk 2 libraries ... Does this also happen with a new second user at this system? Also the test today looks like the display could not be opened at all ... was this debugging done from a virtual terminal or ssh, what is the content of the DISPLAY environment and has the same user a logged in session running at this system? Or at least please describe which desktop environment you are running? I tried to run within a Mate desktop with export QT_QPA_PLATFORMTHEME=gtk2 But still I could not repoduce any fault. Also you might want to install debug symbols also for qt5-style-plugins-dbgsym, libqt5widgets5-dbgsym and supercollider-ide-dbgsym to get a more complete stack. Kind regards, Bernhard