Android Studio: NDK does not belong to any project target,

  android, android-ndk, c++, cmake

I have watched many native c++ projects. And I saw that everyone just simply clicks next and next and it automatically does everything for them.
But when I do exactly the same, it gives me an error in my native CPP.

and my Cmake version is 3.10.2 and NDK is 21.1.6352462cuz these were automatically install these thing for me)
When I look at my includes file in Android view, it showed me that my NDK files does not belong to my project, therefor I cannot call it’s library.
But my code can still run fine, it’s still show "Hello from C++" but the debug always shows error.
This is what my cpp looks like
This is an error that I have

Pls, help me, I have been stuck in this for so long.
Every answer would be appreciated.

Source: Windows Questions C++