SwiftUI Preview for a View with generic views passed as parameters

I would like to use SwiftUI previews for my view, which is built as a container that contains other Views. For example,

public struct ContainerView<Content: View>: View {

    private let title: String
    private let mainView: Content
    
    public init(title: String,
                @ViewBuilder mainView: () -> Content) {
        self.title = title
        self.mainView = mainView()
    }

    public var body: some View {
        VStack {
            Text(title)
            mainView
        }
    }
}

When I add a #Preview to it, it gives this error: Type of expression is ambiguous without a type annotation. Here's an example of a preview:

#Preview {
    let mainView = {
        Text("some view")
    }
    return SummarySectionView(title: "title string",
                              mainView: mainView)
}

Is is a limitation of Swift previews? Should I use another macro/function to display the preview?

Note: this works as soon as a remove the <Content: View> code, with the mainView attribute and so forth...

EDIT: Based on the comments, I was able to find what was wrong. My less contrived code had a second view parameter, like so:

public struct ContainerView<Content: View>: View {

    private let title: String
    private let mainView: Content
    private let secondaryView: Content
    
    public init(title: String,
                @ViewBuilder mainView: () -> Content,
                @ViewBuildeer secondaryView: () -> Content) {
        self.title = title
        self.mainView = mainView()
        self.secondaryView = secondaryView()
    }

    public var body: some View {
        VStack {
            Text(title)
            mainView
            secondaryView
        }
    }
}

Which is fine, except if my 2 views are different, like so:

#Preview {
    let mainView = {
        Text("some view")
    }
    let secondaryView = {
        Button(action: {}, label: {
            Text("Button example")
        })
    }
    return ContainerView(title: "title string",
                              mainView: mainView,
                              secondaryView: secondaryView)
}

Because I thought that mainView and secondaryView were both of type View, it would work, but it does not. Changing the view declaration to this: public struct ContainerView<MainContent: View, SecondaryView: View>: View and making the relevant changes everywhere else resolves my issue.