Mysterious spacing or padding in elements in a VStack in a ScrollView in SwiftUI

If I understand your ultimate goal, it's to have each row bordered above by a dotted line, with no padding between them, like this:

In that case, IMO you should put the lines in a background. For example:

ScrollView {
    VStack(alignment: .leading) {
        ForEach(self.elements, id: \.self) { element in
            HStack {
                Text("\(element.index+1)")
                    .font(.system(.caption, design: .rounded))
                    .frame(width: 32, alignment: .trailing)
                Text(element.element)
                    .font(.system(.caption, design: .monospaced))
                Spacer()
            }
            .background(
                ZStack(alignment: .top) {
                    Color.green
                    GeometryReader { geometry in
                        Path { path in
                            path.move(to: .zero)
                            path.addLine(to: CGPoint(x: geometry.size.width, y: 0))
                        }
                        .strokedPath(StrokeStyle(lineWidth: 1, dash: [1,2]))
                        .foregroundColor(Color.red)
                    }
                }
            )
        }
    }
}

A key point is that ScrollView is not a vertical stacking container. It just takes its content and makes it scrollable. Its content in your code is a ForEach, which generates views; it doesn't really intend to lay them out. So when you combine a ScrollView with a ForEach, nothing is really in charge of placing the views the way you want. To stack views vertically, you want a VStack.

You can apply this to your structure just as well, but adding another VStack, and get the same results:

ScrollView {
    VStack(spacing: 0) { // <---
        ForEach(self.elements, id: \.self) { element in
            VStack(alignment: .leading, spacing: 0) {
                GeometryReader { geometry in
                    Path { path in
                        path.move(to: .init(x: 0, y: 0))
                        path.addLine(to: .init(x: geometry.size.width, y: 0))
                    }
                    .strokedPath(.init(lineWidth: 1, dash: [1,2]))
                }
                .foregroundColor(.red)
                .frame(height: 1)

                HStack {
                    Text("\(element.index+1)")
                        .font(.system(.caption, design: .rounded))
                        .frame(width: 32, alignment: .trailing)
                    Text(element.element)
                        .font(.system(.caption, design: .monospaced))
                        .frame(maxWidth:nil)
                    Spacer()
                }
            }
            .background(Color.green) // <-- Moved
        }
    }
}