Bug 435093

SUMMARY
sddm doesn't look in "/etc/sddm.conf.d" for .conf files.

STEPS TO REPRODUCE
1. Copy /usr/lib/sddm/sddm.conf.d/default.conf into /etc/sddm.conf.d/
2. Make a change you'll be able to recognize (eg. theme)
3. Restart sddm

OBSERVED RESULT
The change in the .conf will not be reflected in sddm.

EXPECTED RESULT
sddm will look in /etc/sddm.conf.d/ and load any configuration in there.

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: Arch Linux
(available in About System)
KDE Plasma Version: 5.21.3
KDE Frameworks Version: 5.80.0
Qt Version: 5.15.2

ADDITIONAL INFORMATION
man sddm.conf.5 mentions the search order for configuration files as:
1) /usr/lib/sddm/sddm.conf.d
2) /etc/sddm.conf.d
3) /etc/sddm.conf

#2 is ignored. If I take that same changed conf from #2 and put that in #3 (where #3 didn't exist previously), it will load it then.