I don’t know if the place to post this question would be in this area.
Some softwares have their icons not very well done in the systray (Windows language).
This is due to the software, and being for Linux and KDE and Gnome existing, the system developer has to program either for one modality or just making the .ico file (I don’t know if this is the extension) for 32bits, since resolves.
If the application doesn’t have a custom icon in your home directory, your DE falls back to the application’s own. Or, at least that’s my understanding.
Also, I almost think an icon can be any image format. Typically icon designers and builders use .svg for Linux, IIRC.