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
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
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.