Result seems OK but icon is not set about xseticon

[xeyownt]

Strange indeed.

Just tried on my Debian Bookworm and it doesn't work either.

Maybe icon management changed in recent distributions.

[ricciolino]

As a workaround I was able to implement the following trick (e.g. launching a gnome-terminal instance from a *.desktop launcher file):

[Desktop Entry]
Name=Live Dmesg
Exec=gnome-terminal --title="Live dmesg" -- bash -c "echo \"Opening dmesg...\"; sleep 0.3; xdotool search --name \"Live dmesg\" set_window --class \"LiveDmesgClass\"; sleep 0.3; sudo dmesg -w"
Icon=/home/ricciolino/.local/share/pixmaps/dmesg.png
Type=Application
StartupNotify=true
StartupWMClass=LiveDmesgClass

As you can see in the "Exec" field, by using the xdotool tool, I am forcing the just opened terminal instance to set its WMClass to match the StartupWMClass launcher property.
Doing so, the launcher icon will match the window icon shown in the "workspace view" and "Alt+Tab switcher view" specified by "Icon" property /home/ricciolino/.local/share/pixmaps/dmesg.png.

--> App search view:

--> Workspace view: