$ ls /usr/share/wallpapers/Bamboo/contents/images/
ls: cannot access '/usr/share/wallpapers/Bamboo/contents/images/': No such file or directory
Well there’s at least one problem. (theme.conf referred to: /usr/share/wallpapers/Bamboo/contents/images/5120x2880.png
btw)
Now that I see that, it’s actually possible I may have deleted it a few weeks back, whichever folder contains the default KDE wallpapers, I deleted that (because KDE’s devs can be retarded sometimes, and they removed the option to set your default wallpaper directory, I didn’t wanna see those default images in my wallpaper list, this was the easiest way to fix that problem)
Edit: I tried setting a custom wallpaper and with that in place sddm seems to be working perfectly (now why on earth would it be borked when there’s no wallpaper? I mean I know why, bogdan explained it, but this just seems like an oversight from the sddm devs. then again they can’t be expected to foresee every scenario of users doing stupid things i suppose)