Icons that use content overlay, leave the icon hidden when using software rendering.
This small change corrects the problem and I did not notice any problems as a result.
A simple test for this is to use the desktop telegram with the plasma in software rendering and taskbar in icon-only mode.
Using OpenGL the icon is displayed and a counter with the number of messages appears overlapping part of the icon, all right.
Using software rendering, the icon disappears when the counter is displayed.
With this modification, the operation using software rendering is corrected.