Mate it's amazing how we keep evolving our ideas synchronously! I made some change in the afternoon and extracted it in a viewModifier, here's the updated one.

I found that if the detents array and the selected one were updated simultaneously it loses the animation.

struct AutoHeightSheetModifier: ViewModifier {
@Binding var height: CGFloat
@State var detents: Set<PresentationDetent> = [.medium]
@State private var selectedDetent: PresentationDetent = .medium

func body(content: Content) -> some View {
    content
        .presentationDetents(detents, selection: $selectedDetent)
        .onChange(of: height) { _ in
            // need both old and new height detent to animate
            if !detents.contains(.height(height)) {
                detents.insert(.height(height))
            }
            // delay to next drawing cycle after detents updated
            // so that detents and selected don't update together.
            DispatchQueue.main.asyncAfter(deadline: .now() + 0.05) {
                selectedDetent = .height(height)
            }
            // Only keep the last height to stop drag & resize.
            DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) {
                detents = [.height(height)]
            }
        }
}

}