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 lock screen and display manager are two separate pieces of software. The display manager runs before a user profile has been selected for graphical login, so it does not have access to your user desktop/display settings
Supposedly both the display manager and greeters have system-wide configuration for this purpose, however. And the issue with notifications and DE overlays are present post login, too.
there’s a button to apply Plasma settings to SDDM for this purpose, it prompts for admin password when you do it, which makes sense