With watchKit 6.1, the full screen setting works properly for me with either a single swiftUI view or single spritekit view (embedded in swiftUI view or WKInterfaceController) but not when part of multiple screens with paged navigation. I could not find any mention in the watchkit documentation about a paging limitation. It also didn't see mention that swiftUI view without spritekit would allow full screen, but it did for me without paging.
I would believe it is not possible except the Apple fitness app seems to workaround this limitation after a workout has been started. The workout paramaters screen is clearly full screen as part of a paged navigation group of 3 screens. I have a similar need for my fitness watch app. Does anyone know how this workaround may have been implemented or have suggestions to try.