I finally understand how to `tableView.separatorInset = .zero` in SwiftUI List (iOS 15+)

ContentView.swift

import SwiftUI
import Introspect // from SwiftPM https://github.com/siteline/SwiftUI-Introspect

struct ContentView: View {
    var body: some View {
        List {
            Text("some")
                .listRowSeparator(.hidden) // disable SwiftUI.List separator
            Text("thing")
                .listRowSeparator(.hidden) // disable SwiftUI.List separator
            Text("some")
                .listRowSeparator(.hidden) // disable SwiftUI.List separator
            Text("thing")
                .listRowSeparator(.hidden) // disable SwiftUI.List separator
        }
        .listStyle(.plain)
        .introspectTableView { tableView in //  enable UITableView separator 🙃
            tableView.separatorStyle = .singleLine
            tableView.separatorInset = .zero
        }
    }
}