Answer
There isn't a single clean LU/view backing the Create User screen — System Info comes back blank there specifically because that screen is a composite view built by joining a dozen or more underlying tables together, so there's no one canonical 'Users' LU to point a custom event at directly. Which specific table you actually need depends on which attribute you want to react to: FND_USER holds the core user record (ID, Active flag, Description); FND_USER_ROLE holds permission-set grants; USER_FINANCE holds company connections; USER_PROFILE holds profile assignment; and USER_ALLOWED_SITE holds site connections — build your custom event against whichever of these specific tables actually owns the attribute you care about, rather than trying to find one all-encompassing Users LU.