iOS 15:

This year Apple introduced a new modifier .listRowSeparator that can be used to style the separators. you can pass .hidden to hide it:

List {
    ForEach(items, id:\.self) { 
        Text("Row \($0)")
            .listRowSeparator(.hidden)
    }
}

iOS 14:

you may consider using a LazyVStack inside a ScrollView instead (because iOS is NOT supporting UIAppearance for SwiftUI lists anymore).

iOS 13:

⚠️ This method is deprecated and it’s not working from iOS 14

There is a UITableView behind SwiftUI’s List for iOS 13. So to remove

Extra separators (below the list):

you need a tableFooterView and to remove

All separators (including the actual ones):

you need separatorStyle to be .none

Example of usage

init() {
    if #available(iOS 14.0, *) { 
        // iOS 14 doesn't have extra separators below the list by default.
    } else {
        // To remove only extra separators below the list:
        UITableView.appearance().tableFooterView = UIView()
    }

    // To remove all separators including the actual ones:
    UITableView.appearance().separatorStyle = .none
}

var body: some View {
    List {
        Text("Item 1")
        Text("Item 2")
        Text("Item 3")
    }
}

Note that a static list doesn’t show extra separators below the list by default