Microsoft wants to make WinUI open source, but there are some major hurdles in the way first including its tie to Windows ...

Read: IntelliSense not working in VS Code 3] Reinstall C/C++ Maybe when installing C/C++ you have made some mistakes due to which Intellisense is unable to pick up libraries.

If a missing Visual C++ library is the cause of the error, you can fix it by installing the Visual C++ Redistributable Packages. Visit Microsoft’s official website and click on the Download button.