Custom icon not displaying for AppImage

Solution 1:

To associate the running application with your .desktop launcher, you will need to explicitly set the StartupWMClass value to the WMClass of your application.

Run the application and determine its wmclass as follows. With Ubuntu 21.10 on Wayland, open the Gnome Shell looking glass by hitting Alt+F2. On the "Windows" tab, find the wmclass. When running Xorg, you can use the xproptool. Run the command xprop | grep WM_CLASS then click the window of your application.

Then edit the .desktoplauncher and add or edit the line

StartupWMClass=<wmclass>

so it indicates the wmclass you found.