Ошибка c2429 для функция языка структурированные привязки нужен флаг компилятора std c 17

Using MS Visual studio I created a solution containing 2 projects called MainProject and CalcProject
MainProject is a console app that references CalcProject and only contains main() in a .cpp file
CalProject is a library and contains a few header files with the following:

Nml.h contains the following:

#include <cstdint>
#include " Ftr.h"
#include " Mtr.h"

namespace CalcProject::measure

{
    class Mtr;
    class Ftr;

    class Nml
    {
    public:
          ...

Ftr.h contains the following:

#include <cstdint>
#include " Mtr.h"
#include " Nml.h"
namespace CalcProject::measure
{
    class Mtr;
    class Nml;

    class Ftr
    {
        ...

Mtr.h contains the following:

#include " Ftr.h"
#include " Nml.h"
namespace CalcProject::measure
{

   class Ftr;
   class Nml;

    class Mtr
    {
        ...

MainProject.cpp contains the following:

#include "pch.h"
#include "Ftr.h"
#include <iostream>
#include <string>

using namespace CalcProject::measure;

int main()
{

When I build the solution I receive the following error
Error C2429 language feature ‘nested-namespace-definition’ requires compiler flag ‘/std:c++17’ MainProject
I tried to resolve this by specifying /std:c++17 in the C++ Language standard in the project properties but the error persists.

How can I fix this? Please advise on a possible solution. I am a beginner and this is my first C++ project using multiple header and cpp files to create a library.

Using MS Visual studio I created a solution containing 2 projects called MainProject and CalcProject
MainProject is a console app that references CalcProject and only contains main() in a .cpp file
CalProject is a library and contains a few header files with the following:

Nml.h contains the following:

#include <cstdint>
#include " Ftr.h"
#include " Mtr.h"

namespace CalcProject::measure

{
    class Mtr;
    class Ftr;

    class Nml
    {
    public:
          ...

Ftr.h contains the following:

#include <cstdint>
#include " Mtr.h"
#include " Nml.h"
namespace CalcProject::measure
{
    class Mtr;
    class Nml;

    class Ftr
    {
        ...

Mtr.h contains the following:

#include " Ftr.h"
#include " Nml.h"
namespace CalcProject::measure
{

   class Ftr;
   class Nml;

    class Mtr
    {
        ...

MainProject.cpp contains the following:

#include "pch.h"
#include "Ftr.h"
#include <iostream>
#include <string>

using namespace CalcProject::measure;

int main()
{

When I build the solution I receive the following error
Error C2429 language feature ‘nested-namespace-definition’ requires compiler flag ‘/std:c++17’ MainProject
I tried to resolve this by specifying /std:c++17 in the C++ Language standard in the project properties but the error persists.

How can I fix this? Please advise on a possible solution. I am a beginner and this is my first C++ project using multiple header and cpp files to create a library.

I aware that someone asked similar question but what I have seen is different error when I try to use c++17 Structure Binding in my code (e.g. for (auto [i, it] = std::tuple{ 0, nodes.begin() }; i < size; i++)), I have already set to use ISO C++17 Standard (/std:c++17) in project properties and checked compiler version.

Ref: Using c++17 ‘structured bindings’ feature in visual studio 2017

Compiler complained
Error C2429 language feature ‘structured bindings’ requires compiler flag ‘/std:c++17’

My Code

TreeNode* ConstructBinaryTree(const int* const intChain, size_t size)
{
    std::list<TreeNode*> nodes;

    for (auto [i, it] = std::tuple{ 0, nodes.begin() }; i < size; i++)
    {
        TreeNode* curr = (it != nodes.end())? *it : nullptr;
        TreeNode* toBeAssiged = new TreeNode(intChain[i]);
        nodes.push_back(toBeAssiged);

        if (curr)
        {
            if (curr->left)
            {
                curr->right = toBeAssiged;
                it++;
            }
            else
            {
                curr->left = toBeAssiged;
            }
        }
    }

    return (nodes.size() == 0)? nullptr : *nodes.begin();
}

According to https://learn.microsoft.com/en-us/cpp/overview/visual-cpp-language-conformance?view=vs-2019

Structure binding should be supported after VS 2017 15.3 17

My compiler version

I aware that someone asked similar question but what I have seen is different error when I try to use c++17 Structure Binding in my code (e.g. for (auto [i, it] = std::tuple{ 0, nodes.begin() }; i < size; i++)), I have already set to use ISO C++17 Standard (/std:c++17) in project properties and checked compiler version.

Ref: Using c++17 ‘structured bindings’ feature in visual studio 2017

Compiler complained
Error C2429 language feature ‘structured bindings’ requires compiler flag ‘/std:c++17’

My Code

TreeNode* ConstructBinaryTree(const int* const intChain, size_t size)
{
    std::list<TreeNode*> nodes;

    for (auto [i, it] = std::tuple{ 0, nodes.begin() }; i < size; i++)
    {
        TreeNode* curr = (it != nodes.end())? *it : nullptr;
        TreeNode* toBeAssiged = new TreeNode(intChain[i]);
        nodes.push_back(toBeAssiged);

        if (curr)
        {
            if (curr->left)
            {
                curr->right = toBeAssiged;
                it++;
            }
            else
            {
                curr->left = toBeAssiged;
            }
        }
    }

    return (nodes.size() == 0)? nullptr : *nodes.begin();
}

According to https://learn.microsoft.com/en-us/cpp/overview/visual-cpp-language-conformance?view=vs-2019

Structure binding should be supported after VS 2017 15.3 17

My compiler version