My bad, after submitting the question I realized I had set the boundarySupplementaryItems property on the entire layout instead of on the sections...

I have the same question/comment.

I watched the SwiftUI Accessibility: Beyond the Basics session and like what I saw, but it did not address my question regarding support for LargeContentViewer on custom views. I have a scenario in one of the apps I am working on - actually trying to decide to do the whole thing in SwiftUI or stick with UIKit for now - that requires some views that cannot change size. Am going through a checklist of components and accessibility features that I feel are must have to aid in my SwiftUI vs UIKit decision.