I’ve had a bit of a search around, but nothing jumped out at me…
I have some applications that have what looks like a default icon in the title bar. Their entries in the task bar/list thing look correct though.
Two that I see now:
Signal, seems to be a wayland icon?
And a “community” wrapper of whatsapp…
Yes, W is the default wayland icon. The X is the default icon for X/X11. That application runs in xwayland mode. From what I’ve seen these are usually application/toolkit problems. Toolkits being what applications use to draw the GUI.
Following the instructions here: Fix Wayland icons of apps after switching to KDE & Wayland [Ubuntu 24.04] · GitHub I pointed to the signal .desktop file and everything works as expected.
I’ve seen similar solutions posted around, but they refer to icons in the task bar. It seems this also solves missing title bar icons.
The whatsapp wrapper is a flatpack. The same solution worked.
I didn’t look too deeply, but it seems like KDE struggles when the window title or class is too different from the name of the .desktop file.
Anyway, now I know.