Recently I’ve installed some SDDM themes for my Arch install using the KDE Store, but whenever I apply them in the SDDM manager the login screen is missing and it prompts me to a black screen with a cursor.
After looking at the sddm.conf file, it appears that it is completely missing, I had to generate a new file using “sddm --example-config”, and it started working again. So far I’ve tried these two themes from the KDE Store:
Sugar Dark
Darkine
Both prompt me to this dark screen, I have not tried any other theme past these.
You’'ll need to find SDDM themes that work in Plasma 6. Most will mention this in the name or description. And even then, I find some do appear to lie about being compatible.
Sugar/Sweet -based themes such as Sugar Dark are old, and definitively don’t work in Plasma 6.
So is Darkine.
About the /etc/sddm.conf being gone. I’ve just noticed on Fedora 42 that the /etc/sddm.conf goes to 0 bytes the instant I install the “sddm” package. I saw this because I was trying to fix the SDDM clock font being too large so I did a “dnf reinstall sddm”. My idea was that the upgrade to KDE 6.4.0 might have messed up sddm so I wanted to start over with it.
The /etc/sddm.conf after dnf reinstall was empty (but exists as a 0 byte file). The actual sddm.conf in the sddm package is 2749 bytes.
I believe that this is the normal behavior, it is not a new thing in my experience here on KDE neon and Kubuntu, and probably the last time I ran Fedora.
SDDM changes are kept in separate files in /etc/sddm.conf.d/, such as kde-settings.conf which is where changes made via System Settings are stored.
To edit the UI, you’d need to edit the theme elements and/or QML files in /usr/share/sddm