Normally I use MATE but now  I switched to Xfce4 for testing and both don't let me run Wonderwall a wunderfull program for searching backgrounds by theme and download them.

The information I get is:
$ LANG=C wonderwall
Gtk-Message: 03:21:39.316: Failed to load module "canberra-gtk-module"
Gtk-Message: 03:21:39.316: Failed to load module "canberra-gtk-module"
Qt: Session management error: None of the authentication protocols specified are supported
QApplication: invalid style override passed, ignoring it.
Fontconfig warning: FcPattern object weight does not accept value [40 210)
Speicherzugriffsfehler (Speicherabzug geschrieben)

I installed this program by snap and I think the programmer is working on Ubuntu.

As far as I understood there may be something wrong with my /etc/X11/xinit/xinitrc.d/40-libcanberra-gtk-module.sh:
#!/bin/sh

case "${DESKTOP_SESSION-}" in
  gnome*) # Done by gnome-settings-daemon
  ;;
  *)
    # Extra check in case DESKTOP_SESSION is not set correctly
    if [ -z "${GNOME_DESKTOP_SESSION_ID-}" ]; then
      GTK_MODULES="${GTK_MODULES:+$GTK_MODULES:}canberra-gtk-module"
      export GTK_MODULES
    fi
  ;;
    # Export GTK_PATH so that GTK+ can find the Xfce theme engine
    #GTK_PATH="$GTK_PATH:/usr/lib/gtk-3.0"
    #export GTK_PATH
esac

On Ubuntu seems not do be X1.../xinit...
I had read that might be something to do with mixed GTK2 and GTK3???

TIA