SwiftUI charts - only show RuleMark below plotted line

I am having some issues with Swift charts. I have the following Chart which has RuleMark. As you can see from the screenshot below the RuleMark extends the length of the screen. I am attempting to only show the mark below the line. Something like this question is asking. If any further clarity is required let me know. The code is below.

struct Item: Identifiable {
    var date: String
    var count: Double
    var id = UUID()
}

var data: [Item] = [
    .init(date: "10AM", count: 5),
    .init(date: "12AM", count: 4),
    .init(date: "2PM", count: 7),
    .init(date: "4PM", count: 2),
    .init(date: "6PM", count: 9)
]

struct ContentView: View {
    var body: some View {
        Chart(data) { item in    
            LineMark(
                x: .value("Date", item.date),
                y: .value("Value", item.count)
            )
            
            PointMark(
                x: .value("Date", item.date),
                y: .value("Value", item.count)
            )
            
            RuleMark(
                x: .value("Value", item.date)
            )
        }
        .chartYAxis(.hidden)
    }
}

Assuming the y axis value of the bottom of the plot is known, you can do:

RuleMark(
    x: .value("Date", item.date),
    yStart: .value("Bottom", 0), // assuming y=0 at the bottom of the chart
    yEnd: .value("Value", item.count)
)

Replace 0 with whatever value the y axis has at the very bottom. Note that you can change the y axis' range using the various chartYScale modifiers.

If the y value of the bottom of the plot is not known (e.g. you are letting SwiftUI automatically decide what scale to use depending on the data), you can use chartBackground/chartOverlay to draw the lines with a Path:

.chartBackground { proxy in
    if let frameAnchor = proxy.plotFrame {
        GeometryReader { geo in
            let frame = geo[frameAnchor]
            ForEach(data) { item in
                if let point = proxy.position(for: (x: item.date, y: item.count)) {
                    Path { p in
                        p.move(to: .init(x: point.x + frame.minX, y: point.y + frame.minY))
                        p.addLine(to: .init(x: point.x + frame.minX, y: frame.maxY))
                    }
                    .stroke(.blue, lineWidth: 1)
                }
            }
        }
    }
}