Some time ago, I tested the xfce4-docklike-plugin (Panel Plugins / xfce4-docklike-plugin · GitLab) instead of the default taskbar.
I installed xfce4-docklike-plugin via qubes-dom0-update.
I don’t know why some AppVM icons load correctly (e.g., Librewolf, Mousepad, xterm) and some don’t (Thunderbird, xfce4-terminal). I haven’t found any correlation as to why this happens.
I have the problem with all AppVMs. Interestingly, the xfce4-terminal icon from dom0 works correctly, but the xfce4-terminal icon from the “personal” AppVM doesn’t – instead, a blue cube appears (as attached).
This has something to do with the desktop files generated in dom0 missing the StartupWMClass.
I was able to fix the broken Firefox icon in docklike by editing its desktop file in dom0: ~/.local/share/applications/org.qubes-os.vm._personal.org.mozilla.firefox.desktop and adding this line below [Desktop Entry]: StartupWMClass=personal:org.mozilla.firefox
and its icon magically appeared.
If you need to restart the panel to see changes you can run xfce4-panel -r.
You can fix the icons of other windows by getting their WMCLASS in dom0: id=$(xdotool selectwindow); xprop -id "$id" WM_CLASS and then clicking on the afflicted application to get its class name. Then add the missing StartupWMClass to their respective desktop files.
Unfortunately these desktop files in dom0 are automatically generated and the changes will get overwritten, so this isn’t really a permanent solution.
