Plasma 6.3 broke klassy … I worked ahead a bit and pulled from the existing PR.
There is also a funny bug I noticed because I have my own theme that explicitly disables the panel shadow (by removing it from the widget svg’s) … this was done in the ‘opaque’ and ‘solid’ subdirectories. And I use a fully solid/opaque panel. Well, after the 6.3 upgrade the shadow reappeared. Only after removing the shadow from the ‘translucent’ subdirectory widgets did it go away again. Thus it would appear that Plasma 6.3 is incorrectly pulling widgets/options from the ‘translucent’ widgets even on non-translucent panels.
Not a big deal in either case, but I leave these notes here in case they mean something to someone.