GoKawiilMicrosoft confirms KB5127648 update can block Smart App Control toggle
Microsoft says its October KB5127648 security update for Windows 11, version 24H2 and later, can leave the Smart App Control option grayed out so it can't be switched on if it was previously off. Devices that already had Smart App Control enabled are unaffected. No permanent fix exists yet, but Microsoft has published registry edits and Group Policy settings administrators can use to restore the toggle.