From their repo:
Plasma Login
Plasma Login provides a display manager for KDE Plasma, forked from SDDM and with an new frontend providing a greeter, wallpaper plugin integration and System Settings module (KCM).
What we want
- Great out-of-box experience in multi-monitor and high DPI and HDR
- Keyboard layout switching
- Virtual keyboards
- Easy Chinese/Japanese/Korean/Vietnamese (CJK) input
- Screen readers for blind people (which then means volume control)
- Remote (VNC/RDP) support from startup
- Deeper Plasma integration including:
- Display and keyboard brightness control
- Full power management
- Pairing trusted bluetooth devices
- Login to known Wi-Fi for remote LDAP
The first one I think is a fundamental limitation in that display preferences by default is per-user. Maybe this makes it work for you? https://feddit.online/post/1350756/comment/6636228
The 24h clock might be similar - check your system-wide locale.
I don’t really have this problem anymore since I got rid of my projector which advertised a resolution it couldn’t handle. Had to login into the void since the login screen never showed up. Looks like this might be fixable nowadays.
The locale is set to American English but the time format is set to German, something the lock screen can handle but SDDM cannot. I also tried applying the Plasma settings to SDDM a few times but it doesn’t really change anything.