SDDM theme is defined in System Settings → Startup → Loginscreen (SDDM). It does not use the Global Theme thing, unless you press the sync button in this screen.
Are you sure you are not talking about the Lockscreen (which is not SDDM)?
SDDM theme is defined in System Settings → Startup → Loginscreen (SDDM). It does not use the Global Theme thing, unless you press the sync button in this screen.
Are you sure you are not talking about the Lockscreen (which is not SDDM)?