这里是一个演示的可能方式。参数的视觉效果，你可以调整为您的需要。
使用Xcode 12 / iOS 14进行测试。

// ... other code
            .fullScreenCover(isPresented: $isLoading) {
                ZStack{
                    Color.black.opacity(0.5).edgesIgnoringSafeArea(.all)
                    VStack {
                        ProgressView()
                        Button("Stop loading") {
                            isLoading.toggle()
                        }
                    }
                }
                .background(BackgroundBlurView())
            }
        }
    }
}

struct BackgroundBlurView: UIViewRepresentable {
    func makeUIView(context: Context) -> UIView {
        let view = UIVisualEffectView(effect: UIBlurEffect(style: .light))
        DispatchQueue.main.async {
            view.superview?.superview?.backgroundColor = .clear
        }
        return view
    }

    func updateUIView(_ uiView: UIView, context: Context) {}
}

在f3dm76上构建答案：
我改变了它，这样后面的内容就不会 Flink （我在fullScreenCover后面加载惰性图像时就发生过这种情况）。另外，我想对全屏内容使用自定义过渡（或者在某些情况下根本没有动画），所以我也用这种方法删除了默认动画。

extension View {

    func transparentNonAnimatingFullScreenCover<Content: View>(isPresented: Binding<Bool>, content: @escaping () -> Content) -> some View {
        modifier(TransparentNonAnimatableFullScreenModifier(isPresented: isPresented, fullScreenContent: content))
    }
    
}

private struct TransparentNonAnimatableFullScreenModifier<FullScreenContent: View>: ViewModifier {
    
    @Binding var isPresented: Bool
    let fullScreenContent: () -> (FullScreenContent)
    
    func body(content: Content) -> some View {
        content
            .onChange(of: isPresented) { isPresented in
                UIView.setAnimationsEnabled(false)
            }
            .fullScreenCover(isPresented: $isPresented,
                             content: {
                ZStack {
                    fullScreenContent()
                }
                .background(FullScreenCoverBackgroundRemovalView())
                .onAppear {
                    if !UIView.areAnimationsEnabled {
                        UIView.setAnimationsEnabled(true)
                    }
                }
                .onDisappear {
                    if !UIView.areAnimationsEnabled {
                        UIView.setAnimationsEnabled(true)
                    }
                }
            })
    }
    
}

private struct FullScreenCoverBackgroundRemovalView: UIViewRepresentable {
    
    private class BackgroundRemovalView: UIView {
        
        override func didMoveToWindow() {
            super.didMoveToWindow()
            
            superview?.superview?.backgroundColor = .clear
        }
        
    }
    
    func makeUIView(context: Context) -> UIView {
        return BackgroundRemovalView()
    }
    
    func updateUIView(_ uiView: UIView, context: Context) {}
    
}

Asperi的答案很漂亮，但如果你想让背景透明而不模糊，这里有你可以修改它的方法。为了方便起见，我还把代码移到了一个修改器中。（xcode 13.3，iOS 15.4.1）

extension View {

    func transparentFullScreenCover<Content: View>(isPresented: Binding<Bool>, content: @escaping () -> Content) -> some View {
        fullScreenCover(isPresented: isPresented) {
            ZStack {
                content()
            }
            .background(TransparentBackground())
        }
    }
}

struct TransparentBackground: UIViewRepresentable {

    func makeUIView(context: Context) -> UIView {
        let view = UIView()
        DispatchQueue.main.async {
            view.superview?.superview?.backgroundColor = .clear
        }
        return view
    }

    func updateUIView(_ uiView: UIView, context: Context) {}
}

也可以使用“材质”背景类型：

ZStack{
   ...
}
.background(.ultraThinMaterial)

有关更多用法，请参阅文档：https://developer.apple.com/documentation/swiftui/material

我发现这个更清洁的解决方案的 Flink 问题在清晰的背景。

struct ClearBackgroundView: UIViewRepresentable {
    func makeUIView(context: Context) -> UIView {
        return InnerView()
    }
    
    func updateUIView(_ uiView: UIView, context: Context) {
    }
    
    private class InnerView: UIView {
        override func didMoveToWindow() {
            super.didMoveToWindow()
            
            superview?.superview?.backgroundColor = .clear
        }
        
    }
}

用途

PresenterView()
    .fullScreenCover(isPresented: $isPresented) {
        PresentedView()
            .background(ClearBackgroundView())
    }