The default scaling method works well enough for most wallpapers, however, Plasma also supports animated gif wallpapers, most of which tend to be very low resolution pixel art and meant to be upscaled using a sharp method as opposed to the smooth scaling Plasma currently does, which results in said wallpapers looking pretty bad currently

Allowing the user to simply switch between smooth and sharp scaling would completely solve this issue as the user could just choose whatever scaling type best fits the wallpaper they want (sharp for pixel art wallpapers, smooth for pretty much anything else)