This post is from the Activity iPhone Duo UIKit Q&A.
The same .pageSheet is edge-to-edge on the folded phone and an inset sheet on the unfolded display, because the size class is regular. Our home sheet used to include its own tab bar so it could cover the real one. On the inner display that produces two tab bars. Should a phone-style edge-to-edge sheet on the inner display be requested with a specific modalPresentationStyle or UISheetPresentationController flag, rather than inferring it from “sheet width ≈ window width”?