Using a KDE Slimbook II to log in I got locked out and eventually realised the Num Lock was on so half the keyboard was typing numbers. This laptop has no LEDs on the keys and a systray indicator is present instead to show to the user if caps lock or num lock are on. SDDM has a caps lock indicator but no num lock indicator.

Full size keyboards will typically have num lock on all the time and that's expected so num lock indicator here would just be annoying, but laptop keyboards not. So it probably needs a user configurable option to show the num lock indicator