c++20 and c++11 standards both specified in tasks.json, still won't work?

I'm learning C++ using Visual Studio Code. I'm starting to pull my hair out trying to figure why the compiler won't recognize C++11 standards. The code + .json file + error are as follows:

#include <iostream>
#include <vector>
using namespace std;

int main() {

    vector <int> vector_numbers;

    for (int i : vector_numbers) {
        vector_numbers[1] = i + 1;
    }

    for (int i : vector_numbers) {
        cout << "The vector element at index [" << i << "] is " << vector_numbers.at(i) << endl;
    }

    return 0;
}

The contents of "args" parameter in tasks.json is

            "args": [
                "-std=c++11",
                "-std=c++17",
                "-std=c++20",
                "-stdlib=libc++",
                "-fcolor-diagnostics",
                "-fansi-escape-codes",
                "-g",
                "${file}",
                "-o",
                "${fileDirname}/${fileBasenameNoExtension}"
            ]

and error is:

<REDACTED> % cd "<REDACTED PATH>" && g++ Vectors.cpp -o Vectors && "<REDACTED PATH>"Vectors
Vectors.cpp:9:16: warning: range-based for loop is a C++11 extension [-Wc++11-extensions]
    for (int i : vector_numbers) {
               ^
Vectors.cpp:13:16: warning: range-based for loop is a C++11 extension [-Wc++11-extensions]
    for (int i : vector_numbers) {
               ^
2 warnings generated.