I ran into this issue on my newly installed laptop (Guix System).
Even after reconfiguring to 15a523ea213065c275e4852673cbb27c72c0ad87
(current master as of today), the screen stayed black and SDDM didn't start.
My sddm configuration:
```
(service sddm-service-type
(sddm-configuration
(display-server "wayland")))
```
So in the end I switched back to GDM which works :)
~Jonathan
