In iOS 27, of a UIViewController, how do I set the edge effect of a title? What do I need to call?

In iOS 27, for a UIViewController you don’t set the title’s edge effect directly on the view controller. The relevant change is around navigation bar scroll edge effects.

What you need to call is the new-ish navigation item configuration for the bar’s behavior:

• barMinimizationBehavior to control whether the navigation bar minimizes
• barMinimizationSafeAreaAdjustment if you manage safe-area insets yourself
• For the scroll edge effect, review any custom styling you may have set, especially if you previously forced it to .soft or .automatic

From the WWDC session:

• The system’s automatic scroll edge effect no longer switches between the older soft and hard styles; it now uses its own visuals.
• If you previously overrode the style from automatic, that choice should be reevaluated.

So, if your question is “what do I need to call?” the answer is: there isn’t a new UIViewController API to set the title edge effect directly—you should configure the navigation item / navigation bar and let the system handle the updated scroll edge effect, or revisit any custom scroll edge effect styling you already apply.

Relevant session: Modernize your UIKit app.