Three-Way comparison operator(<=>) not defined for std::string

Question

I am attempting to make use of c++20's new Three-Way operator(<=>) capabilities in my programs, but it appears that this operator is not defined for strings, as this program

#include <compare>
#include <string>

using namespace std;

int main()
{

    string a = "a";
    string b = "b";
    auto x = (a <=> b);

    return 0;
}

produces this error:

Error   C2676   binary '<=>': 'std::string' does not define this operator or a conversion to a type acceptable to the predefined operator

However, according to cppreference, this operation should be defined in c++20: https://en.cppreference.com/w/cpp/string/basic_string/operator_cmp

Three-Way comparison operator works fine with primitive types, as changing the first two variables to int compiles without issue, additionally default-implemented Three-Way comparison operator is working correctly with classes, but only when those classes contain primitive types only. The same problem is happening with std::vector as well, which should support Three-Way comparison operator from what I understand.

I am using cmake, and I have correctly set the standard to C++ 20 as far as I am aware

cmake_minimum_required (VERSION 3.8)

set(CMAKE_CXX_STANDARD 20)
set(CMAKE_CXX_STANDARD_REQUIRED True)

I am compiling using MSVC in visualstudio