wallpaper is not scaled properly on wayland when in multiscreen configuration when one monitor is standard dpi and the other one is hidpi. picture on hidpi monitor seems 1/4 of the full picture.
I can confirm that, I have the same issue. I use Arch, FullHD and HiDPI screen. On HiDPI I got 2x scale.
Created attachment 114102 [details] Trying to set wallpaper. It appears to be buggy on simple wallpaper config too.
Does it fix itself after you run "plasmashell --replace"?