I just updated my system... at first I thought something is broken because instead of a nice-to-look-at, smooth login screen I loved and which matched my Breeze DARK them, I was greeted by an ugly solid color of Windows-blue with some white elements on it...

Now even Windows has a nice login screen with background image and what you do??? remove the image in favour of an 1994 looking solid Windows blue... what the hell is wrong with you people?

At least please supply the previous one as an option. Or someone please tell me how do I hack it back because the current one is just wrong on every possible levels.

There are a few SDDM Themes here: https://store.kde.org/browse/cat/101/

You can also tweak the sddm background wallpaper from the systemsettings.
If you really want the old one which I can't recommend (as of the code changes not estatics) you can browse the git repo here and see if you find the commit before the theme was changed

KDE SDDM theme background

Both the plasma 5.8 sddm theme and the older versions are supporting the theme background images.



If the sddm kcm module is installed: KDE System Settings > Startup and Shutdown > Login Screen (SDDM)

Arch

If you are using Arch Linux



there is a sddm wiki: https://wiki.archlinux.org/index.php/SDDM

Arch has an archive: https://wiki.archlinux.org/index.php/Arch_Linux_Archive

You could download the plasma-workspace 5.7.5 package, unpack it. Extract the breeze sddm theme. Rename it breeze-575 (remember to edit the metadata.desktop).



and drop it to the /usr/share/sddm/themes/.





More

SDDM Theming: https://github.com/sddm/sddm/wiki/Theming
Video background: viewtopic.php?f=289&t=131783#p364567
Changing KDE Breeze SDDM theme time format: viewtopic.php?f=289&t=130484&p=365600#p365600