In current Rawhide, after an install from the KDE live image, the desktop selector drop-down box on the left hand side of SDDM seems blank. It's just all grey, with the drop-down arrow on the end. There is no text - it should say 'Plasma'.
If you click on the arrow, you get a black box with a grey border and no visible text. If you mouse over this and then mouse away, it becomes a grey box with 'Plasma' visible in black text, and the cursor (bizarrely) becomes the X fallback 'cross' cursor. If you hover the mouse over the box, it turns back into the black box, and the cursor fixes itself; as soon as you move the mouse away from the box again, it goes back to being the grey box with 'Plasma' visible, and the cursor breaks again.
This seems to be resolved with current Rawhide.