My own header file is not recognized

Hello,
I had my own header file cbuff.h with data structure, which I want to include in main.c but when I do it, the main function is not able to find this header file. May you help? Here are the screenshots.

cbuff
cbuff2

Active project is selected correctly according the the project environment switcher?

A normal ‘build’ or Cmd+Shift+P → Rebuild IntelliSense does not resolve the issue?

Thank you, I switched the project enviroment as it listed under the link which you attached and it works. Thank you for your help.