List with ForEach Enumeration

When I enumerate an array of objects with ForEach, I often wonder how I use the array. For example, I have the following lines of code.

import SwiftUI

struct ContentView: View {
	@State var checkItems: [CheckItem] = [
		.init("Susan"),
		.init("Meagan"),
		.init("Daniel")
	]
	var body: some View {
		List() {
			ForEach(0..<checkItems.count, id: \.self) { index in
				HStack {
					Image(systemName: !checkItems[index].selected ? "circle" : "checkmark.circle.fill")
						.resizable()
						.scaledToFit()
						.frame(height: 24)
						.foregroundColor(!checkItems[index].selected ? .gray : .blue)
						.onTapGesture {
							checkItems[index].selected.toggle()
						}
					Text(checkItems[index].name)
				}
			}
		}
	}
}

struct CheckItem: Identifiable, Hashable {
	var id = UUID()
	var selected: Bool
	var name: String

	init(_ name: String) {
		self.selected = false
		self.name = name
	}
}

The code works as shown in the following image.

In the following lines of code, I'm enumerating the same array in a slightly different fashion.

struct ContentView: View {
	@State var checkItems: [CheckItem] = [
		.init("Susan"),
		.init("Meagan"),
		.init("Daniel")
	]
	var body: some View {
		List() {
			ForEach(checkItems, id: \.id) { item in
				HStack {
					Image(systemName: !item.selected ? "circle" : "checkmark.circle.fill")
						.resizable()
						.scaledToFit()
						.frame(height: 24)
						.foregroundColor(!item.selected ? .gray : .blue)
						.onTapGesture {
							//item.selected.toggle() // Cannot use mutating member on immutable value: 'item' is a 'let' constant
						}
					Text(item.name)
				}
			}
		}
	}
}

And I get an error in the line inside the onTapGesture guy. I wonder why the first section of code works and why second section doesn't? Muchos thankos.