Did you use the default (Crystal) icon theme before? It seems this affects only those who use it. I use DarkGlass_Reworked, maybe because of that I had no such problem.
Hmmm. I went into the 11.4_x86/3.5 (from 11.4 repo) system I genned earlier this week. Changed from the default theme (which I believe is "crystal-SUSE") to "Plastik". Before this change, neither Kcontrol nor icons.desktop worked. After the change, icons.desktop worked, but Kcontrol still comes up blank as always. Even changed the icon theme (to KDE-Classic) ... no difference.
Interesting tidbit: when you select Plastik as the theme, it automagically switched to the "crystal-SVG" ison theme, and I couldn't see any material impact. So, changed back to that after KDE-Classic.