Why can't I use the thread library?

Question

C++ / C#

I'm trying to use the thread library, but it gives an error:
error: this_thread' has not been declared

Code:

#include <iostream>
#include<thread>
#include <chrono>
using namespace std;

int main()
{
    cout << this_thread::get_id()<<endl;
}

I went to the file with the library and almost all the code is inactive there (in vs code it is highlighted less brightly than the working code).