For the part 3 challenge, I'm adding a navigaiton bar item to toggle between showing mission dates and the crew name. As soon as I add the trailing item, the style of the table view is changed from the default plain style to some other style that doesnt seem to match any other one (like grouped, inset grouped etc)

I am using Xcode 12 beta 6 so I dont know if that could be the cause.

Before adding a navigation bar item

struct ContentView: View {
    let astronauts: [Astronaut] = Bundle.main.decode(file: "astronauts.json")
    let missions: [Mission] = Bundle.main.decode(file: "missions.json")

    var body: some View {
        NavigationView {
            List(missions) { mission in
                NavigationLink(destination: MissionView(mission: mission)) {
                    MissionRowView(mission: mission)
                }
            }
            .navigationBarTitle("Moonshot")
        }
    }
}

After adding a navigation bar item

struct ContentView: View {
    let astronauts: [Astronaut] = Bundle.main.decode(file: "astronauts.json")
    let missions: [Mission] = Bundle.main.decode(file: "missions.json")

    @State var showCrew = false

    var body: some View {
        NavigationView {
            List(missions) { mission in
                NavigationLink(destination: MissionView(mission: mission)) {
                    MissionRowView(mission: mission, showCrew: showCrew)
                }
            }
            .navigationBarTitle("Moonshot")
            .navigationBarItems(trailing: Button("Toggle", action: { showCrew.toggle() }))
        }
    }
}

Adding in .listStyle(PlainListStyle()) after the List fixes it but it seems like it shouldnt be neede in the first place.

It might have to do with your MissionRowView. Could you share the code?